Table of Contents
This document describes yabasic. You will find information about the yabasic interpreter (the program yabasic under Unix or yabasic.exe under Windows) as well as the language (which is, of course, a sort of basic) itself.
This document applies to version 2.90 of yabasic
However, it does not contain the latest news about yabasic or a FAQ. As such information tends to change rapidly, it is presented online only at www.yabasic.de.
Although basic has its reputation as a language for beginning programmers, this is not an introduction to programming at large. Rather this text assumes, that the reader has some (moderate) experience with writing and starting computer programs.
yabasic is a traditional basic interpreter. It understands most of the typical basic-constructs, like goto, gosub, line numbers, read, data or string-variables with a trailing '$'. But on the other hand, yabasic implements some more advanced programming-constructs like subroutines or libraries (but not objects). yabasic works much the same under Unix and Windows.
yabasic puts emphasis on giving results quickly and easily; therefore simple commands are provided to open a graphic window, print the graphics or control the console screen and get keyboard or mouse information. The example below opens a window, draws a circle and prints the graphic:
open window 100,100 open printer circle 50,50,40 text 10,50,"Press any key to get a printout" clear screen inkey$ close printer close window
This example has fewer lines, than it would have in many other programming languages. In the end however yabasic lacks behind more advanced and modern programming languages like C++ or Java. But as far as it goes it tends to give you results more quickly and easily.
Once, yabasic has been set up correctly, there are three ways to start it:
Right click on your desktop: The desktop menu appears with a submenu named new. From this submenu choose yabasic. This will create a new icon on your desktop. If you right click on this icon, its context menu will appear; choose Execute to execute the program.
As a variant of the way described above, you may simply create a file with the ending .yab (e.g. with your favorite editor). Everything else then works as described above.
From the start-menu: Choose yabasic from your start-menu. A console-window will open and you will be asked to type in your program. Once you are finished, you need to type return twice, and yabasic will parse and execute your program.
This is not the preferred way of starting yabasic ! Simply because the program, that you have typed, can not be saved and will be lost inevitably ! There is no such thing as a save-command and therefore no way to conserve the program, that you have typed. This mode is only intended for quick hacks, and short programs.
Under Windows yabasic will mostly be invoked by double-clicking on an appropriate icon; this way you do not have a chance to specify any of the command line options below. However, advanced users may change the librarypath in the registry, which has the same effect as specifying it as an option on the command line.
See the chapter on options for a complete list of all options, either on Unix or Windows.
Like every other icon under Windows, the icon of every yabasic-program has a context menu offering the most frequent operations, that may be applied to a yabasic-program.
This will invoke yabasic to execute your program. The same happens, if you double click on the icon.
notepad will be invoked, allowing you to edit your program.
This will present the embedded documentation of your program. Embedded documentation is created with the special comment doc.
If your system administrator (vulgo root) has installed yabasic correctly, there are three ways to start it:
You may use your favorite editor (emacs, vi ?) to put your program into a file (e.g. foo). Make sure that the very first line starts with the characters '#!' followed by the full pathname of yabasic (e.g. '#!/usr/local/bin/yabasic'). This she-bang-line ensures, that your Unix will invoke yabasic to execute your program (see also the entry for the hash-character). Moreover, you will need to change the permissions of your yabasic-program foo, e.g. chmod u+x foo. After that you may invoke yabasic to invoke your program by simply typing foo (without even mentioning yabasic). However, if your PATH-variable does not contain a single dot ('.') you will have to type the full pathname of your program: e.g. /home/ihm/foo (or at least ./foo).
Save your program into a file (e.g. foo) and type yabasic foo. This assumes, that the directory, where yabasic resides, is contained within your PATH-variable.
Finally your may simply type yabasic (maybe it will be necessary to include its full pathname). This will make yabasic come up and you will be asked to type in your program. Once you are finished, you need to type return twice, and yabasic will parse and execute your program.
This is not the preferred way of starting yabasic ! Simply because the program, that you have typed, can not be saved and will be lost inevitably ! There is no such thing as a save-command and therefore no way to conserve the program, that you have typed. This mode is only intended for quick hacks, and short programs, i.e. for using yabasic as some sort of fancy desktop calculator.
yabasic accepts a number of options on the command line.
See chapter on options for a complete list of all options, either on Unix or Windows.
If you want to set some options once for all, you may put them into your X-Windows resource file. This is usually the file .Xresources or some such within your home directory (type man X for details).
Here is a sample section, which may appear within this file:
yabasic*foreground: blue yabasic*background: gold yabasic*geometry: +10+10 yabasic*font: 9x15
This will set the foreground color of the graphic-window to blue and the background color to gold. The window will appear at position 10,10 and the text font will be 9x15.
Here are the options, that yabasic accepts on the command line (both under Unix and Windows).
All the options below may be abbreviated (and one hyphen may be dropped), as long as the abbreviation does not become ambiguous. For example, you may write -e instead of --execute.
--help or -?
Prints a short help message, which itself describes two further help-options.
--version
Prints the version of yabasic.
--infolevel INFOLEVEL
Change the infolevel of yabasic, where INFOLEVEL can be one of debug, note, warning, error, fatal and bison (the default is warning). This option changes the amount of debugging-information yabasic produces. However, normally only the author of yabasic (me !) would want to change this.
--execute A-PROGRAM-AS-A-SINGLE-STRING
With this option you may specify some yabasic-code to be executed right away. This is useful for very short programs, which you do not want to save to a file. If this option is given, yabasic will not read any code from a file. E.g.
yabasic -e 'for a=1 to 10:print a*a:next a'
prints the square numbers from 1 to 10.
--bind NAME-OF-STANDALONE-PROGRAM
Create a standalone program (whose name is specified by NAME-OF-STANDALONE-PROGRAM) from the yabasic-program, that is specified on the command line. See the section about creating a standalone-program for details.
--geometry +X-POSITION+Y-POSITION
Sets the position of the graphic window, that is opened by open window (the size of this window, of course, is specified within the open window-command). An example would be -geometry +20+10, which would place the graphic window 10 pixels below the upper border and 20 pixels right of the left border of the screen. This value cannot be changed, once yabasic has been started.
-fg FOREGROUND-COLOR or --foreground FOREGROUND-COLOR
Unix only. Define the foreground color for the graphics-window (that will be opened with open window). The usual X11 color names, like red, green, … are accepted. This value cannot be changed, once yabasic has been started.
-bg BACKGROUND-COLOR or --background BACKGROUND-COLOR
Unix only. Define the background color for the graphics-window. The usual X11 color names are accepted. This value cannot be changed, once yabasic has been started.
--display X11-DISPLAY-SPECIFICATION
Unix only. Specify the display, where the graphics window of yabasic should appear. Normally this value will be already present within the environment variable DISPLAY.
--font NAME-OF-FONT
Under Unix. Name of the font, which will be used for text within the graphics window.
--font NAME-OF-FONT
Under Windows. Name of the font, which will be used for graphic-text; can be any of decorative, dontcare, modern, roman, script, swiss. You may append a fontsize (measured in pixels) to any of those fontnames; for example -font swiss30 chooses a swiss-type font with a size of 30 pixels.
--docu NAME-OF-A-PROGRAM
Print the embedded documentation of the named program. The embedded documentation of a program consists of all the comments within the program, which start with the special keyword doc. This documentation can also be seen by choosing the corresponding entry from the context-menu of any yabasic-program.
--check
Check for possible compatibility problems within your yabasic-program. E.g. this option reports, if you are using a function, that has recently changed.
--librarypath DIRECTORY-WITH-LIBRARIES
Change the directory, wherein libraries will be searched and imported (with the import-command). See also import for more information about the way, libraries are searched.
--
Do not try to parse any further options; rather pass the subsequent words from the commandline to yabasic.
In addition to the usual decimal notation (e.g. 1234), yabasic also supports numeric literals with base 2 or 16; examples are 0b10011 (the number 19, written with base 2) or 0x34AF (the number 13487, written with base 16) respectively. Please note that these numbers (apart from the way you write them into your program) are no different from “ordinary” numbers and can be used in any place, where a normal number with base 10 would fit. E.g. you may compute the sine sin(0b110); so the base 2 (or 16) is just a different way of representation.
See also adding code during execution.
This chapter presents some general concepts and terms, which deserve a description on their own, but are not associated with a single command or function in yabasic. Most of these topics do not lend themselves to be read alone, rather they might be read (or skimmed) as background material if an entry from the alphabetical list of commands refers to them.
Logical shortcuts are no special language construct and there is no keyword for them; they are just a way to evaluate logical expressions. Logical expressions (i.e. a series of conditions or comparisons joined by and or or) are only evaluated until the final result of the expression can be determined. An example:
if (a<>0 and b/a>2) print "b is at least twice as big as a"
The logical expression a<>0 and b/a>2 consists of two comparisons, both of which must be true, if the print statement should be executed. Now, if the first comparison (a<>0) is false, the whole logical expression can never be true and the second comparison (b/a>2) need not be evaluated.
This is exactly, how yabasic behaves: The evaluation of a composed logical expressions is terminated immediately, as soon as the final result can be deduced from the already evaluated parts.
In practice, this has the following consequences:
If two or more comparisons are joined with and and one comparison results in false, the logical expression is evaluated no further and the overall result is false.
If two or more comparisons are joined with or and one comparison results in true, the logical expression is evaluated no further and the result is true.
“Nice, but whats this good for ?”, I hear you say. Well, just have another look at the example, especially the second comparison (b/a>2); dividing b by a is potentially hazardous: If a equals zero, the expression will cause an error and your program will terminate. To avoid this, the first part of the comparison (a<>0) checks, if the second one can be evaluated without risk. This pre-checking is the most common usage and primary motivation for logical shortcuts (and the reason why most programming languages implement them).
Well, bottomline there is no difference or distinction between conditions and expressions, at least as yabasic is concerned. So you may assign the result of comparisons to variables or use an arithmetic expression or a simple variable within a condition (e.g. within an if-statement). So the constructs shown in the example below are all totally valid:
input "Please enter a number between 1 and 10: " a rem Assigning the result of a comparison to a variable okay=a>=1 and a<=10 rem Use a variable within an if-statement if (not okay) error "Wrong, wrong !"
So conditions and expressions are really the same thing (at least as long as yabasic is concerned). Therefore the terms conditions and expression can really be used interchangeably, at least in theory. In reality the term condition is used in connection with if or while whereas the term expression tends to be used more often within arithmetic context.
Yabasic, of course, allows to compare strings with strings and numbers with numbers; <, <=, > and >= compare their left-hand side to their right-hand side as usual; nothing new here and examples can be found throughout this manual.
More interesting, the equality-operator (for numbers as well as for strings) can be written in two different ways: either as = (traditional) or as == (more modern). The second form has the advantage of beeing visually distinct from the assignment-operator, which is the single =. One may argue therefore, that using == results in code, that is easier to understand and read; This manual however sticks to tradition and mostly uses the single = for equality-check.
Finally, inequality can be checked with <> or !=; both operators behave identically and so it is only a matter of taste, which one to use.
References on arrays are the only way to refer to an array as a whole and to pass it to subroutines or functions like arraydim or arraysize.
While (for example) a(2) designates the second element of the array a, a() (with empty braces) refers to the array a itself. a() is called an array reference. A nice example is the bultin function split, that accepts an array-reference and modifies the content of this array.
You may also pass to and use array reference within your own subroutines; these subroutines will then be able to modify the array you have passed in often this is intended.
Passing an array reference does not create a copy of the array; this has some interesting consequences:
Speed and space: Creating a copy of an array would be a time and memory consuming operation; passing just a reference is cheap and fast.
Returning many values: A subroutine, that wants to give back more than one value, may require an array reference among its arguments and then store its many return values within this array. This is the only way to return more than one value from a subroutine.
The following program creates two subroutines (print_words and upcase_words), that operate on an array of words (words$() below):
dim words$(4)
for i=1 to 4
read words$(i)
next i
print_words(words$())
upcase_words(words$())
print_words(words$())
sub print_words(w$())
local i
for i=1 to arraysize(w$(),1)
print w$(i)," ";
next i
print
end sub
sub upcase_words(w$())
local i
for i=1 to arraysize(w$(),1)
w$(i) = upper$(w$(i))
next i
end sub
data "case","does","not","matter"
If you run this program, you will get this output:
case does not matter
CASE DOES NOT MATTER
As you probably know, windows uses the character '\' to separate the directories within a pathname; an example would be C:\yabasic\yabasic.exe (the usual location of the yabasic executable). However, the very same character '\' is used to construct escape sequences, not only in yabasic but in most other programming languages.
Therefore the string "C:\t.dat" does not specify the file t.dat within the directory C:; this is because the sequence '\t' is translated into the tab-character. To specify this filename, you need to use the string "C:\\t.dat" (note the double slash '\\').
Escape-sequences are the preferred way of specifying 'special' characters. They are introduced by the '\'-character and followed by one of a few regular letters, e.g. '\n' or '\r' (see the table below).
Escape-sequences may occur within any string at any position; they are replaced at parsetime (opposed to runtime), i.e. as soon as yabasic discovers the string, with their corresponding special character. As a consequence of this len("\a") returns 1, because yabasic replaces "\a" with the matching special character just before the program executes.
Table 6.1. Escape sequences
| Escape Sequence | Matching special character |
|---|---|
\n
|
newline |
\t
|
tabulator |
\v
|
vertical tabulator |
\b
|
backspace |
\r
|
carriage return |
\f
|
formfeed |
\a
|
alert (i.e. a beeping sound) |
\\
|
backslash |
\'
|
single quote |
\"
|
double quote |
\x
HEX
|
chr$(HEX) (see below) |
Note, that an escape sequences of the form \xHEX allows one to encode arbitrary
characters as long as you know their position (as a hex-number) within the
ascii-charset:
For example \x012 is transformed into the character chr$(18) (or chr$(dec("12",16)). Note that \x requires a
hexa-decimal number (and the hexadecimal string "12" corresponds to the decimal number 18).
Normally, you write programs in yabasic and specify all the necessary logic and calculations within your program. Once you are done, you invoke it, probably multiple times; and while it is running, it does not change.
However, there are some commands within yabasic, that allow to blur the line between writing and execution. Namely eval, eval$, compile, execute and execute$ allow to create and execute new yabasic-code while your program is running. This comes in handy, if the code to be used comes from the user of your program and will only be known after your program has started. A simple example is the yabasic-code to calculate the maximum of a user-supplied expression within a given range; find it as an example for eval. In the same way, one may write a program to plot an arithmetic function, whose definition is entered by the user.
Note: Even if the commands listed above allow to change the yabasic-program, that is currently running, the file where the program is stored, does not change. Therefore, the changes to the running program are not permanent.
The most simple functions are eval and eval$; they compile an expression (with a numeric or string result), e.g. and execute it right away. The compiled code is remembered, so that it need not be compiled again, when the sames expression is executed again; this caters efficiency. However these functions only accept a single expression and nothing else.
If you need more complex computation and logic, the process needs to be split: First create a new subroutine with the compile-command, then execute this subroutine (maybe multiple times) via execute or execute$. This allows to use the broad logic available in subroutines (e.g. conditions, loops, local variables or even other subroutines) and therefore much more complex calculations than with eval. If you want to use compile multiple times within your program (e.g. in a loop), you may want to enumerate the functions you create to avoid name-clashes (as shown in the examples of compile).
To invoke the subroutines created, you need to execute them with execute or execute$, which require the name of the function (a string) as their first argument.
Sometimes you may want to give one of your yabasic-programs to other people. However, what if those other people do not have yabasic installed ? In that case you may create a standalone-program from your yabasic-program, i.e. an executable, that may be executed on its own, standalone, even (and especially !) on computers, that do not have yabasic installed. Having created a standalone program, you may pass it around like any other program (e.g. one written in C) and you can be sure that your program will execute right away.
Such a standalone-program is simply created by copying the full yabasic-interpreter and your yabasic-program (plus all the libraries that it may import) together into a single, new program, whose name might be chosen at will (under windows of course it should have the ending .exe). If you decide to create a standalone-program, there are three facilities in yabasic, that you may use:
The bind-command, which does the actual job of creating the standalone program from the yabasic-interpreter and your program.
The command-line Option --bind (see options), which does the same from the command-line.
The special peek("isbound"), which may be used to check, if the yabasic-program containing this peek is bound to the interpreter as part of a standalone program.
With these bits you know enough to create a standalone-program. Actually there are two ways to do this: on the command line and from within your program.
Let's say you have the following very simple program within the file foo.yab:
print "Hello World !"
Normally you would start this yabasic-program by typing yabasic foo.yab and as a result the string Hello World ! would appear on your screen. However, to create a standalone-program from foo.yab you would type:
yabasic -bind foo.exe foo.yab
This command does not execute your program foo.yab but rather create a standalone-program foo.exe. Note: under Unix you would probably name the standalone program foo or such, omitting the windows-specific ending .exe.
Yabasic will confirm by printing something like: ---Info: Successfully bound 'yabasic' and 'foo.yab' into 'foo.exe'.
After that you will find a program foo.exe (which must be made executable with the chmod-command under Unix first). Now, executing this program foo.exe (or foo under Unix) will produce the output Hello World !.
This newly created program foo.exe might be passed around to anyone, even if he does not have yabasic installed.
It is possible to write a yabasic-program, that binds itself to the yabasic-interpreter. Here is an example:
if (!peek("isbound")) then
bind "foo"
print "Successfully created the standalone executable 'foo' !"
exit
endif
print "Hello World !"
If you run this program (which may be saved in the file foo.yab) via yabasic foo.yab, the peek("isbound") in the first line will check, if the program is already part of a standalone-program. If not (i.e. if the yabasic-interpreter and the yabasic-program are separate files) the bind-command will create a standalone program foo containing both. As a result you would see the output Successfully created the standalone executable 'foo' !. Note: Under Windows you would probably choose the filename foo.exe.
Now, if you run this standalone executable foo (or foo.exe), the very same yabasic-program that is shown above will be executed again. However, this time the peek("isbound") will return TRUE and therefore the condition of the if-statement is false and the three lines after then are not executed. Rather the last print-statement will run, and you will see the output Hello World !.
That way a yabasic-program may turn itself into a standalone-program.
The new standalone program will be at least as big as the interpreter itself, which is typically a few hundred kilobytes.
There is no easy way to extract your yabasic-program from within the standalone program: If you ever want to change it, you should keep it around as a separate file.
If a new version of yabasic becomes available, you might want to recreate your standalone program to take advantage of bugfixes and improvements.
Under Unix, depending on the way yabasic has been built, this feature might have been disabled; the error message in this case will read like this build of yabasic does not support calling foreign libraries. To resolve this issue, you are invited to contact the maintainer.
This is interesting, but somewhat advanced stuff. You will need a good understanding of various concepts of the C-language, especially pointers and structures as well as allocating and freeing blocks of memory. Please be aware, that mistakes or errors during calls to foreign functions or buffers may easily crash yabasic.
Yabasic allows to employ functionality from
an external library; i.e. from a library, which is not written in yabasic, but rather in C; such a library is called a foreign library, as opposed to a library written in yabasic itself. Calling out to a foreign library can be useful, if such a library provides functionality, that can not be replicated in yabasic itself and for which a commandline-interface (which could be used via system) does not exist or is too cumbersome or slow. Examples would be libraries libVLC or libcurl which offer the functionality of vlc or curl to other programs, especially programs written in yabasic.
The foreign function interface of yabasic relies on the great libffi-library, a library making it easy to call other libraries dynamicaaly and the established standard for this task.
Libraries (e.g. libcurl) are meant to provide functionality to other programs (here: yabasic and your yabasic-program). Libraries and programs must be linked together; this can happen either statically at compile-time or dynamically during the excution of the program. For yabasic as the program, static linking happens at the time, yabasic itself is build, whereas dynamic linking happen during the execution and under control of your yabasic-program. So the foreign function interface deals with dynamic (or runtime) linking to external libraries. This linking is done by yabasic behind the scene, when you invoke foreign_function_call; this function, after loading the library, directly calls the specified function therein.
Which functions are available differs from library to library and you should already have this information before you try the library with yabasic.
If you want to use a function from a foreign library, you will need to deal with the fact, that each function requires several parameters and returns exactly one. These parameters have a wide variety of types which need to be mapped to the two types (numbers and strings) known by yabasic. Here are the types available for foreign functions, grouped by the way, they are handled in yabasic:
uint8,int8,uint16,int16,uint32,int32,uint64,int64,float,double,char,short,int,long
In C all these types are used to represent numbers (integer or floating point) with various degrees of precision. When invoking foreign_function_call you need to pass strings, which specify the right type as well as the actual yabasic-value, which will then be converted accordingly. Which types a foreign function expects can be looked up e.g. from its manpage.
string
Strings for foreign functions directly map to strings of yabasic. So if you specify this type for a parameter of a foreign function, the matching value is simply a yabasic string. If you specify string as the return value of a foreign function you should use the variant of calling it, which returns a string, i.e. foreign_function_call$.
buffer
You should specify a buffer as the type of a parameter or the return type, if the foreign function expects a structure or a pointer to a memory area; see structures and buffers for details.
This first example prints the cosine of 2, not by using yabasics own cos-function but by calling out to the standard C-library:
if peek$("os")="windows" then
lib$ = "msvcrt.dll"
else
lib$ = "libm.so.6"
endif
print "cos(2): ",foreign_function_call(lib$,"double","cos","double",2)
The first lines determine the name of the library, which is different under Unix and Windows. The call to foreign_function_call than just states the name of the library, the return type ("double") of the function and then its name ("cos"), as well as type and value (2) of its argument. The final result -0.416147 then is the same as from the the internal cos-function, which is no surprise, because yabasic is already statically linked to the standard C-library and uses its function to compute the cosine.
A second example:
if peek$("os")="windows" then
lib$ = "msvcrt.dll"
else
lib$ = "libm.so.6"
endif
print foreign_function_call$(lib$,"string","strstr","string","foobar","string","ob","options","copy_string_result")
This example calls the strstr-function from the standard C-library; this function accepts two string arguments and returns a string, which is the first (if any) appearance of the second string within the first one (remark: this function makes more sense in C than in yabasic). Please note the option "copy_string_result", which advices yabasic to return a copy of the result of strstr; otherwise your program might crash, because strstr simply returns a pointer to a part of its first argument, a string that will later be freed by yabasic.
This example is windows only; it shows a standard Windows message box with the given title and message:
message_box("Hello World !","Message from yabasic")
sub message_box(message$, title$)
msgptr$ = foreign_buffer_alloc$(len(message$)+1)
foreign_buffer_set msgptr$, 0, message$
titleptr$ = foreign_buffer_alloc$(len(title$)+1)
foreign_buffer_set titleptr$, 0, title$
hwnd$ = foreign_function_call$("user32.dll", "buffer", "GetActiveWindow")
ret = foreign_function_call("user32.dll", "int32", "MessageBoxA", "buffer", hwnd$, "buffer", msgptr$, "buffer", titleptr$, "uint32", 0)
foreign_buffer_free msgptr$
foreign_buffer_free titleptr$
return ret
end sub
The relevant Windows-function MessageBoxA is found within the library user32.dll; most of the example deals with properly allocating, handling and freeing buffers to hold the supplied text-snippets. Thanx to Jean-Marc Duro for this example.
A remark on libffi: this is the library which allows yabasic to call functions from other libraries libffi is used by many other programming-languages for the same purpose; in yabasic it is linked statically (rather than dynamically) so that its functionality is available right from the start. Summing up: libffi itself need not be loaded but helps to call functions from other loaded libraries.
Here is the sequence of events during a foreign function call (e.g. foreign_function_call):
Yabasic parses the type specifications and argument values provided and collects the necessary information for libffi.
The named library is loaded with the appropriate call (which is different under Windows and Unix). This step might easily fail, e.g. if you misspelled the name of the library or your system cannot find the library.
With the help of libffi the named function is invoked.
If you specified the option unload_library, the library that has been loaded is unloaded again.
The return value of the function is converted to a form suitable for yabasic and your program continues.
Errors are reported during every step.
Yabasics functions for dealing with foreign libraries start with foreign_function or foreign_buffer (e.g. foreign_buffer_alloc). To help in typing, these names can all be abbreviated by contracting foreign_function into frnfn and foreign_buffer into frnbf. In the examples below, both forms appear.
The C-language provides a wide variety of simple datatypes (like numbers an strings) and allows to aggregate simple datatypes to structures such a structure contains a set of simple types arranged without overlap (but sometimes with gaps). Yabasic on itself does not know the internals of a structure but rather treats it as a uniform buffer. Structure and buffer are just flipsides of the same memory area viewed either from C or yabasic. For your yabasic-program a buffer is represented by a handle, which is just a simple printable string (containing the size and the memory adress).
The detailed knowledge about the simple types within a structure must be coded into your program, which uses the command (or function) foreign_buffer_set and foreign_buffer_get. Both functions require type and offset (which needs to be looked up in documentation of the foreign library) of the simple type within the structure and a handle to the buffer, which contains the structure.
Beeing essentially a memory area, a buffer is created with foreign_buffer_alloc and destroyed with foreign_buffer_free if needed no more.
Besides representing a structure, a buffer can also provide room to store raw areas of memory for use by the foreign library; example might be image- or sound-content.
The example below deals with the time functions from the standard C-library; some of them deal with the tm structure for keeping the segmented time; to understand the example it is good to have the tm-structure at hand; see below. In addition it might be helpful to consult the manpages of the various C-functions (e.g. localtime)involved.
struct tm {
int tm_sec; /* Seconds (0-60) */
int tm_min; /* Minutes (0-59) */
int tm_hour; /* Hours (0-23) */
int tm_mday; /* Day of the month (1-31) */
int tm_mon; /* Month (0-11) */
int tm_year; /* Year - 1900 */
int tm_wday; /* Day of the week (0-6, Sunday = 0) */
int tm_yday; /* Day in the year (0-365, 1 Jan = 0) */
int tm_isdst; /* Daylight saving time */
};
The example plays with the two forms of keeping the time, either as unix-time (number of seconds since epoch) or as a segmented time (sec, min, etc.). The six steps are each introduced by comments, please see below.
# First: Determine the correct library depending on OS
#
if peek$("os")="windows" then
lib$ = "msvcrt.dll"
else
lib$ = "libm.so.6"
endif
# Second: Get the unix-time
#
# time() has a pointer argument to store the result (in addition to returning it)
# we pass NULL, so only the return value is relevant
#
null$ = foreign_buffer_alloc$(-1)
now = foreign_function_call(lib$,"int","time","buffer",null$)
print "Seconds since the epoch: ",now
# Third: Convert the unix-time to a segmented time
#
# localtime() does not accept the time-value as an argument, but rather requires a pointer
# to the time-value, so we construct a buffer for one int and put in our value
now$ = foreign_buffer_alloc$(foreign_function_size("int"))
foreign_buffer_set now$,0,"int",now
# Dump the buffer for educational purpose
print "Dump of buffer: ",foreign_buffer_dump$(now$)
# localtime() returns a structure with the componentes (year, day, sec, etc.) as elements
local$ = foreign_function_call$(lib$,"buffer","localtime","buffer",now$)
# Fourth: Get the current year from the resulting buffer
#
# assuming, that year is the sixth element of the structure
# so offset is 5
offset = 5 * foreign_function_size("int")
year = foreign_buffer_get(local$,offset,"int")
print "Current year: ", year + 1900
# Fifth: manipulate the segmented time
#
# set year to something else
foreign_buffer_set local$,offset,"int",year-50
# Sixth: convert time-structure from localtime into ascii
#
print "50 years back: ", foreign_function_call$(lib$,"string","asctime","buffer",local$)
On my computer this program produces the following output:
Seconds since the epoch: 1559014899 Dump of buffer: F3ADEC5C Current year: 2019 50 years back: Tue May 28 05:41:39 1969
This final example just invokes libcurl to report its version. This is somewhat involved, because the matching function curl_version_info (see its man-page) returns a structure, which contains a pointer to a string, as can be seen from the structures definition:
typedef struct {
CURLversion age; /* see description below */
const char *version; /* human readable string */
unsigned int version_num; /* numeric representation */
const char *host; /* human readable string */
int features; /* bitmask, see below */
char *ssl_version; /* human readable string */
long ssl_version_num; /* not used, always zero */
const char *libz_version; /* human readable string */
const char * const *protocols; /* protocols */
... /* more lines omitted */
} curl_version_info_data;
Please note, that the yabasic-code below uses abbreviations (e.g. frnfn_call instead of foreign_function_call.
# Get structure with version info
info$ = frnfn_call$("libcurl.so.4","buffer","curl_version_info","int",1)
# dump it for reference
print frnbf_dump$(info$,32)
# assume, that the pointer to version string is at offset 8
sinfo$ = frnbf_get_buffer$(info$,8)
# print readable version
print frnbf_get$(sinfo$,0,10)
The printing of frnbf_dump gives a hint on the internal offsets within the structure and helps to determine that offset of 8 for the next call.
On my system this program produces 7.61.1 for the version of curl.
and
print-command to place the output at a specified position
abs() — returns the absolute value of its numeric argument
y=abs(x)
acos() — returns the arcus cosine of its numeric argument
x=acos(angle)
acos is the arcus cosine-function, i.e. the inverse of the cos-function. Or, more elaborate: It Returns the angle (in radians, not degrees !), which, fed to the cosine-function will produce the argument passed to the acos-function.
and — logical and, used in conditions
if a and b … while a and b …
Used in conditions (e.g within if, while or until) to join two expressions. Returns true, if and only if its left and right argument are both true and false otherwise.
Note, that logical shortcuts may take place.
and() — the bitwise arithmetic and
x=and(a,b)
Used to compute the bitwise and of both its argument. Both arguments are treated as binary numbers (i.e. a sequence of digits 0 and 1); a bit of the resulting value will then be 1, if both arguments have a 1 at this position in their binary representation.
Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to and.
arraydim() — returns the dimension of the array, which is passed as an array reference
a=arraydim(b())
If you apply the arraydim()-function on a one-dimensional array (i.e. a vector) it will return 1, on a two-dimensional array (i.e. a matrix) it will return 2, and so on.
This is mostly used within subroutines, which expect an array among their parameters. Such subroutines tend to use the arraydim-function to check, if the array which has been passed, has the right dimension. E.g. a subroutine to multiply two matrices may want to check, if it really is invoked with two 2-dimensional arrays.
dim a(10,10),b(10)
print arraydim(a()),arraydim(b())
This will print 2 1, which are the dimension of the arrays a() and b(). You may check out the function arraysize for a full example.
arraysize() — returns the size of a dimension of an array
x=arraysize(a(),b)
The arraysize-function computes the size of the specified dimension of a given array. Here, size stands for the maximum number, that may be used as an index for this array. The first argument to this function must be an reference to an array, the second one specifies, which of the multiple dimensions of the array should be taken to calculate the size. Please note, that arraysize returns the value that has been used in the actual dim-statement, the real (internal) size of the array is allocated one larger in each dimension to have a first element at index 0; however this is not reflected by the output of arraysize.
An Example involving subroutines: Let's say, an array has been declared as dim a(10,20) (that is a two-dimensional array or a matrix). If this array is passed as an array reference to a subroutine, this sub will not know, what sort of array has been passed. With the arraydim-function the sub will be able to find the dimension of the array, with the arraysize-function it will be able to find out the size of this array in its two dimensions, which will be 10 and 20 respectively.
Our sample array is two dimensional; if you envision it as a matrix this matrix has 10 lines and 20 columns (see the dim-statement above. To state it more formally: The first dimension (lines) has a size of 10, the second dimension (columns) has a size of 20; these numbers are those returned by arraysize(a(),1) and arraysize(a(),2) respectively. Refer to the example below for a typical usage.
rem
rem This program adds two matrices elementwise.
rem
dim a(10,20),b(10,20),c(10,20)
rem initialization of the arrays a() and b()
for y=1 to 10:for x=1 to 20
a(y,x)=int(ran(4)):b(y,x)=int(ran(4))
next x:next y
matadd(a(),b(),c())
print "Result:"
for x=1 to 20
for y=10 to 1 step -1
print c(y,x)," ";
next y
print
next x
sub matadd(m1(),m2(),r())
rem This sub will add the matrices m1() and m2()
rem elementwise and store the result within r()
rem This is not very useful but easy to implement.
rem However, this sub excels in checking its arguments
rem with arraydim() and arraysize()
local x:local y
if (arraydim(m1())<>2 or arraydim(m2())<>2 or arraydim(r())<>2) then
error "Need two dimensional arrays as input"
endif
y=arraysize(m1(),1):x=arraysize(m1(),2)
if (arraysize(m2(),1)<>y or arraysize(m2(),2)<>x) then
error "The two matrices cannot be added elementwise"
endif
if (arraysize(r(),1)<>y or arraysize(r(),2)<>x) then
error "The result cannot be stored in the third argument"
endif
local xx:local yy
for xx=1 to x
for yy=1 to y
r(yy,xx)=m1(yy,xx)+m2(yy,xx)
next yy
next xx
end sub
asc() — accepts a string and returns the position of its first character within the ascii charset
a=asc(char$)
The asc-function accepts a string, takes its first character and looks it up within the ascii-charset; this position will be returned. The asc-function is the opposite of the chr$-function. There are valid uses for asc, however, comparing strings (i.e. to bring them into alphabetical sequence) is not among them; in such many cases you might consider to compare strings directly with <, = and > (rather than converting a string to a number and comparing this number).
asin() — returns the arcus sine of its numeric argument
angle=asin(x)
acos is the arcus sine-function, i.e. the inverse of the sin-function. Or, more elaborate: It Returns the angle (in radians, not degrees !), which, fed to the sine-function will produce the argument passed to the asin-function.
at() — can be used in the print-command to place the output at a specified position
clear screen … print at(a,b) print @(a,b)
The at-clause takes two numeric arguments (e.g. at(2,3)) and can be inserted after the print-keyword. at() can be used only if clear screen has been executed at least once within the program (otherwise you will get an error).
The two numeric arguments of the at-function may range from 0 to the width of your terminal minus 1, and from 0 to the height of your terminal minus 1; if any argument exceeds these values, it will be truncated accordingly. However, yabasic has no influence on the size of your terminal (80x25 is a common, but not mandatory), the size of your terminal and the maximum values acceptable within the at-clause may vary. To get the size of your terminal you may use the peek-function: peek("screenwidth") returns the width of your terminal and peek("screenheight") its height.
atan() — returns the arctangent of its numeric argument
angle=atan(a,b) angle=atan(a)
atan is the arctangent-function, i.e. the inverse of the tan-function. Or, more elaborate: It Returns the angle (in radians, not degrees !), which, fed to the tan-function will produce the argument passed to the atan-function.
The atan-function has a second form, which accepts two arguments: atan(a,b) which is (mostly) equivalent to atan(a/b) except for the fact, that the two-argument-form returns an angle in the range -π to π, whereas the one-argument-form returns an angle in the range -π/2 to π/2. To understand this you have to be good at math.
bell
beep)
not
rectangle
color — change color for background of graphic window
backcolour red,green,blue backcolour "red,green,blue"
Change the color, that becomes visible, if any portion of the window is erased, e.g. after clear window or clear line. Note however, that parts of the window, that show the old background color will not change.
As with the color-command, the new background color can either be specified as a triple of three numbers or as a single string, that contains those three numbers separated by commas.
Note, that the command backcolor can be written as backcolour too and vice versa.
beep — ring the bell within your computer; a synonym for bell
beep
The bell-command rings the bell within your computer once. This command is not a sound-interface, so you can neither vary the length or the height of the sound (technically, it just prints \a). bell is exactly the same as beep.
bin$() — converts a number into a sequence of binary digits
hexadecimal$=bin$(decimal)
The bin$-function takes a single numeric argument an converts it into a string of binary digits (i.e. zeroes and ones). If you pass a negative number to bin$, the resulting string will be preceded by a '-'.
If you want to convert the other way around (i.e. from binary to decimal) you may use the dec-function.
bind() — binds a yabasic-program and the yabasic-interpreter together into a standalone program
bind("foo.exe")
The bind-command combines your own yabasic-program (plus all the libraries it does import) and the interpreter by copying them into a new file, whose name is passed as an argument. This new program may then be executed on any computer, even if it does not have yabasic installed.
Please see the section about creating a standalone-program for details.
if (!peek("isbound")) then
bind "foo"
print "Successfully created the standalone executable 'foo' !"
exit
endif
print "Hello World !"
This example creates a standalone program foo from itself.
The section about creating a standalone-program, the peek-function and the command line options.
bitnot() — the bitwise arithmetic not
x=bitnot(a)
This function is used to compute the bitwise not of its single argument. The argument is treated as binary number (i.e. a sequence of digits 0 and 1); a bit of the resulting value will be 1, if the argument has a 0 at this position in its binary representation; if the bit in the argument is 1, the bit in the result will be 0.
Note, that its argument is silently converted to a positive integer value and that negative numbers have their own binary representation and may lead to unexpected results when passed to bitnot.
A note on naming: This one-argument-function is named bitnot to distinguish it from the one-argument-function not, which operates on logical expressions. For the similar functions and and or this distinction between logical and bitwise function is done implicitly through the number of arguments (1 and 2, respectively).
break — breaks out of one or more loops or switch statements
break
break 2
break transfers control immediately outside the enclosing loop or switch statement. This is the preferred way of leaving a such a statement (rather than goto, which is still possible in most cases). An optional digit allows one to break out of multiple levels, e.g. to leave a loop from within a switch statement. Please note, that only a literal (e.g. 2) is allowed at this location.
for a=1 to 10
break
print "Hi"
next a
while 1
break
print "Hi"
wend
repeat
break
print "Hi"
until 0
switch 1
case 1:break
case 2:case 3:print "Hi"
end switch
This example prints nothing at all, because each of the loops (and the switch-statement) does an immediate break (before it could print any "Hi").
circles, rectangles or triangles
line-command
for-, do-, repeat- or while-loop
case — mark the different cases within a switch-statement
switch a case 1 case 2 … end switch … switch a$ case "a" case "b" … end switch
ceil() — compute the ceiling for its (float) argument
print ceil(x)
The ceil-function returns the smallest integer number, that is larger or equal than its argument.
chomp$() — remove a single trailing newline from its string-argument; if the string does not end in a newline, the string is returned unchanged
print chomp$("Hallo !\n")
The chomp$-function checks, if its string-argument ends in a newline and removes it eventually; for this purpose chomp$ can replace an if-statement. This can be especially useful, when you deal with input from external sources like system$.
You may apply chomp$ freely, as it only acts, if there is a newline to remove; note however, that user-input, that comes from the normal input-statement, does not need such a treatment, because it already comes without a newline.
The following yabasic-program uses the unix-command whoami to get the username of the current user in order to greet him personally. This is done twice: First with the chomp$-function and then again with with an equivalent if-statement:
print "Hello " + chomp$(system$("whoami")) + " !"
user$ = system$("whoami")
if (right$(user$,1)="\n") user$=left$(user$,len(user$)-1)
print "Hello again " + user$ + " !"
chr$() — accepts a number and returns the character at this position within the ascii charset
character$=chr$(ascii)
The chr$-function is the opposite of the asc-function. It looks up and returns the character at the given position within the ascii-charset. It's typical use is to construct nonprintable characters which do not occur on your keyboard.
Nevertheless you won't use chr$ as often as you might think, because the most important nonprintable characters can be constructed using escape-sequences using the \-character (e.g. you might use \n instead of chr$(10) wherever you want to use the newline-character).
circle — draws a circle in the graphic-window
circle x,y,r clear circle x,y,r fill circle x,y,r clear fill circle x,y,r
The circle-command accepts three parameters: The x- and y-coordinates of the center and the radius of the circle.
Some more observations related with the circle-command:
The graphic-window must have been opened already.
The circle may well extend over the boundaries of the window.
If you have issued open printer before, the circle
will finally appear in the printed hard copy of the window.
fill circle will draw a filled (with black ink) circle.
clear circle will erase (or clear) the outline of the circle.
clear fill circle or fill clear circle will erase the full area of the circle.
open window 200,200
for n=1 to 2000
x=ran(200)
y=ran(200)
fill circle x,y,10
clear fill circle x,y,8
next n
This code will open a window and draw 2000 overlapping circles within. Each circle is drawn in two steps: First it is filled with black ink (fill circle x,y,10), then most of this circle is erased again (clear fill circle x,y,8). As a result each circle is drawn with an opaque white interior and a 2-pixel outline (2-pixel, because the radii differ by two).
clear — erase circles, rectangles or triangles
clear rectangle 10,10,90,90 clear fill circle 50,50,20 clear triangle 10,10,20,20,50,30
May be used within the circle, rectangle or triangle command and causes these shapes to be erased (i.e. be drawn in the colour of the background).
fill can be used in conjunction with and wherever the fill-clause may appear. Used alone, clear will erase the outline (not the interior) of the shape (circle, rectangle or triangle); together with fill the whole shape (including its interior) is erased.
clear screen — erases the text window
clear screen
clear screen erases the text window (the window where the output of print appears).
It must be issued at least once, before some advanced screen-commands (e.g. print at or inkey$) may be called; this requirement is due to some limitations of the curses-library, which is used by yabasic under Unix for some commands.
clear window — clear the graphic window and begin a new page, if printing is under way
clear window
clear window clears the graphic window. If you have started printing the graphic via open printer, the clear window-command starts a new page as well.
open window 200,200
open printer "t.ps"
for a=1 to 10
if (a>1) clear window
text 100,100,"Hallo "+str$(a)
next a
close printer
close window
This example prints 10 pages, with the text "Hello 1", "Hello 2", … and so on. The clear screen-command clears the graphics window and starts a new page.
close — close a file, which has been opened before
close filenum close # filenum
The close-command closes an open file. You should issue this command as soon as you are done with reading from or writing to a file.
close curve — close a curve, that has been drawn by the line-command
new curve line to x1,y1 … close curve
The close curve-command closes a sequence of lines, that has been drawn by repeated line to-commands.
close printer — stops printing of graphics
close printer
The close printer-command ends the printing graphics. Between open printer and close printer everything you draw (e.g. circles, lines …) is sent to your printer. close printer puts an end to printing and will make your printer eject the page.
close window — close the graphics-window
close window
The close window-command closes the graphics-window, i.e. it makes it disappear from your screen. It includes an implicit close printer, if a printer has been opened previously.
color — change color for any subsequent drawing-command
colour red,green,blue colour "red,green,blue"
Change the color, in which lines, dots, circles, rectangles or triangles are drawn. The color-command accepts three numbers in the range 0 … 255 (as in the first line of the synopsis above). Those numbers specify the intensity for the primary colors red, green and blue respectively. As an example 255,0,0 is red and 255,255,0 is yellow.
Alternatively you may specify the color with a single string (as in the second line of the synopsis above); this string should contain three numbers, separated by commas. As an example "255,0,255" would be violet. Using this variant of the colour-command, you may use symbolic names for colours:
open window 100,100 yellow$="255,255,0" color yellow$ text 50,50,"Hallo"
, which reads much clearer.
open window 255,255
for x=10 to 235 step 10:for y=10 to 235 step 10
colour x,y,0
fill rectangle x,y,x+10,y+10
next y:next x
This fills the window with colored rectangles. However, none of the used colours contains any shade of blue, because the color-command has always 0 as a third argument.
Note, that the command color can be written as colour too and vice versa.
compile — compile a string with yabasic-code on the fly
compile(code$)
This is an advanced command (closely related with the execute-command). It allows you to compile a string of yabasic-code (which is the only argument). Afterwards the compiled code is a normal part of your program.
Note, that there is no way to remove the compiled code.
compile("sub mysub(a):print a:end sub")
mysub(2)
This example creates a function named mysub, which simply prints its single argument.
This next example combines the functions compile and execute:
count = 1
subname$ = "foo" + str$(count)
compile("sub "+ subname$ + "(a):print a:end sub")
execute(subname$,2)
This example creates and executes a function, whose name (foo1) is stored within the variable subname$; the newly created function simply prints its single argument. This example could be executed multiple times within a single yabasic-program, simply by incrementing the variable count; by doing that, multiple subroutines (foo1, foo2, …) could be created and executed in succession.
continue — start the next iteration of a for-, do-, repeat- or while-loop
continue
You may use continue within any loop to start the next iteration immediately. Depending on the type of the loop, the loop-condition will or will not be checked. Especially: for- and while-loops will evaluate their respective conditions, do- and repeat-loops will not.
Remark: Another way to change the flow of execution within a loop, is the break-command.
do-loop
data — introduces a list of data-items
data 9,"world" … read b,a$
The data-keyword introduces a list of comma-separated list of strings or numbers, which may be retrieved with the read-command.
The data-command itself does nothing; it just stores data. A single data-command may precede an arbitrarily long list of values, in which strings or numbers may be mixed at will.
yabasic internally uses a data-pointer to keep track of the current location within the data-list; this pointer may be reset with the restore-command.
do
restore
for a=1 to 4
read num$,num
print num$,"=",num
next a
loop
data "eleven",11,"twelve",12,"thirteen",13,"fourteen",14
This example just prints a series of lines eleven=11 up to fourteen=14 and so on without end.
The restore-command ensures that the list of data-items is read from the start with every iteration.
date$ — returns a string with various components of the current date
a$=date$
The date$-function (which must be called without parentheses; i.e. date$() would be an error) returns a string containing various components of a date; an example would be 4-05-27-2004-Thu-May. This string consists of various fields separated by hyphens ("-"):
The day within the week as a number in the range 0 (=Sunday) to 6 (=Saturday) (in the example above: 4, i.e. Thursday).
The month as a number in the range 1 (=January) to 12 (=December) (in the example: 5 which stands for May).
The day within the month as a number in the range 1 to 31 (in the example: 27).
The full, 4-digit year (in the example: 2004, which reminds me that I should adjust the clock within my computer …).
The abbreviated name of the day within the week (Mon to Sun).
The abbreviated name of the month (Jan to Dec).
Therefore the whole example above (4-05-27-2004-Thu-May) would read: day 4 in the week (counting from 0), May 27 in the year 2004, which is a Thursday in May.
Note, that all fields within the string returned by date$ have a fixed with (numbers are padded with zeroes); therefore it is easy to extract the various fields of a date format with mid$.
rem Two ways to print the same ...
print mid$(date$,3,10)
dim fields$(6)
a=split(date$,fields$(),"-")
print fields$(2),"-",fields$(3),"-",fields$(4)
This example shows two different techniques to extract components from the value returned by date$. The mid$-function is the preferred way, but you could just as well split the return-value of date$ at every "-" and store the result within an array of strings.
dec() — convert a base 2 or base 16 number into decimal form
a=dec(number$) a=dec(number$,base)
The dec-function takes the string-representation of a base-2 or base-16 (which is the default) number and converts it into a decimal number. The optional second argument (base) might be used to specify a base other than 16. However, currently only base 2 or base 16 are supported. Please note, that for base 16 and 2 you may write literals in the usual way, by preceding them with 0x or 0b respectively, e.g. like
print 0xff + 0b11
; this may save you from applying the dec altogether.
default — mark the default-branch within a switch-statement
switch a+3 case 1 … case 2 … default … end switch
The default-clause is an optional part of the switch-statement (see there for more information). It introduces a series of statements, that should be executed, if none of the cases matches, that have been specified before (each with its own case-clause).
So default specifies a default to be executed, if none of the explicitly named cases matches; hence its name.
print "Please enter a number between 0 and 6,"
print "specifying a day in the week."
input d
switch d
case 0:print "Monday":break
case 1:print "Tuesday":break
case 2:print "Wednesday":break
case 3:print "Thursday":break
case 4:print "Friday":break
case 5:print "Saturday":break
case 6:print "Sunday":break
default:print "Hey you entered something invalid !"
end switch
This program translates a number between 0 and 6 into the name of a weekday; the default-case is used to detect (and complain about) invalid input.
dim — create an array prior to its first use
dim array(x,y) dim array$(x,y)
The dim-command prepares one or more arrays (of either strings or numbers) for later use. This command can also be used to enlarges an existing array.
When an array is created with the dim-statement, memory is allocated and all elements are initialized with either 0 (for numerical arrays) or "" (for string arrays). Please be aware, that the dim reserves room for one element more than actually specified, e.g. dim(10) reserves memory for 11 elements. This makes it possible to access element 0 as well as element 10, which serves the conventions of C as well as basic.
If the array already existed, and the dim-statement specifies a larger size than the current size, the array is enlarged and any old content is preserved. But note, that dim cannot be used to shrink an array: If you specify a size, that is smaller than the current size, the dim-command does nothing.
Finally: To create an array, that is only known within a single subroutine, you should use the command local, which creates local variables as well as local arrays.
dim a(5,5)
for x=1 to 5:for y=1 to 5
a(x,y)=int(ran(100))
next y:next x
printmatrix(a())
dim a(7,7)
printmatrix(a())
sub printmatrix(ar())
local x,y,p,q
x=arraysize(ar(),1)
y=arraysize(ar(),2)
for q=1 to y
for p=1 to y
print ar(p,q),"\t";
next p
print
next q
end sub
This example creates a 2-dimensional array (i.e. a matrix) with the dim-statement and fills it with random numbers. The second dim-statement enlarges the array, all new elements are filled with 0.
The subroutine printmatrix just does, what its name says.
do — start a (conditionless) do-loop
do … loop
Starts a loop, which is terminated by loop; everything between do and loop will be repeated forever. This loop has no condition, so it is an infinite loop; note however, that a break- or goto-statement might be used to leave this loop anytime.
doc — special comment, which might be retrieved by the program itself
doc This is a comment docu This is another comment
Introduces a comment, which spans up to the end of the line. But other than the rem-comment, any docu-comment is collected within the special docu$-array and might be retrieved later on. Moreover you might invoke yabasic -docu foo.yab on the command line to retrieve the embedded documentation within the program foo.yab.
Instead of doc you may just as well write docu or even documentation.
rem Hi, this has been written by me
rem
doc This program asks for a number and
doc prints this number multiplied with 2
rem
rem Print out the above message
rem
for a=1 to arraysize(docu$(),1):print docu$(a):next a
rem Read and print the number
input "Please input a number: " x
print x*2
This program uses the comments within its code to print out a help message for the user; if you run this program, you get this output:
This program asks for a number and prints this number multiplied with 2 Please input a number: 2 4
The contents of the doc-lines are retrieved from the docu$-array; if you do not want a comment to be collected within this array, use the rem-statement instead.
docu$ — special array, containing the contents of all docu-statement within the program
a$=docu$(1)
Before your program is executed, yabasic collects the content of all the doc-statements within your program within this 1-dimensional array (well only those within the main-program, libraries are skipped).
You may use the arraysize function to find out, how many lines it contains.
docu
docu This program reads two numbers
docu and adds them.
docu
rem retrieve and print the embedded documentation
for a=1 to arraysize(docu$(),1)
print docu$(a)
next a
input "First number: " b
input "Second number: " c
print "The sum of ",b," and ",c," is ",b+c
This program uses the embedded documentation to issue a usage-message.
dot — draw a dot in the graphic-window
dot x,y clear dot x,y
Draws a dot at the specified coordinates within your graphic-window. If printing is in effect, the dot appears on your printout too.
Use the functions peek("winheight") or peek("winwidth") to get the size of your window and hence the boundaries of the coordinates specified for the dot-command.
if-statement
if-statement
if-statement
2.71828182864
else — mark an alternative within an if-statement
if (…) then … else … endif
The else-statement introduces the alternate branch of an if-statement. I.e. it starts the sequence of statements, which is executed, if the condition of the if-statement is not true.
elsif — starts an alternate condition within an if-statement
if (…) then … elseif (…) … elsif (…) then … else … endif
The elsif-statement is used to select a single alternative among a series of choices.
With each elsif-statement you may specify a condition, which is tested, if the main condition (specified with the if-statement) has failed. Note that elsif might be just as well written as elseif.
Within the example below, two variables a and b are tested against a range of values. The variable a is tested with the elsif-statement. The very same tests are performed for the variable b too; but here an involved series of if-else-statements is employed, making the tests much more obscure.
input "Please enter a number: " a
if (a<0) then
print "less than 0"
elseif (a<=10) then
print "between 0 and 10"
elsif (a<=20)
print "between 11 and 20"
else
print "over 20"
endif
input "Please enter another number: " b
if (b<0) then
print "less than 0"
else
if (b<=10) then
print "between 0 and 10"
else
if (b<=20) then
print "between 11 and 20"
else
print "over 20"
endif
endif
endif
Note, that the very same tests are performed for the variables a and b, but can be stated much more clearly with the elsif-statement.
Note, that elsif might be written as elseif too, and that the keyword then is optional.
end — terminate your program
end
Terminate your program. Much (but not exactly) like the exit command.
Note, that end may not end your program immediately; if you have opened a window or called clear screen, yabasic assumes, that your user wants to study the output of your program after it has ended; therefore it issues the line ---Program done, press RETURN--- and waits for a key to be pressed. If you do not like this behaviour, consider using exit.
endif — ends an if-statement
if (…) then … endif
The endif-statement closes (or ends) an if-statement.
Note, that endif may be written in a variety of other ways: end if, end-if or even fi.
The endif-statement must be omitted, if the if-statement does not contain the keyword then (see the example below). Such an if-statement without endif extends only over a single line.
end sub — ends a subroutine definition
sub foo(…) … end sub
Marks the end of a subroutine-definition (which starts with the sub-keyword).
The whole concept of subroutines is explained within the entry for sub.
eof — check, if an open file contains data
open 1,"foo.bar" if (eof(1)) then … end if
The eof-function checks, if there is still data left within an open file. As an argument it expects the file-number as returned by (or used within) the open-function (or statement).
As a special case, if the argument is zero: test if input from stdin is available.
eor() — compute the bitwise exclusive or of its two arguments
print eor(a,b)
The eor-function takes two arguments and computes their bitwise exclusive or. I.e. treat each arguments as a sequence of bits and compare theses two sequences bit by bit to produce the result. If the bits from the arguments are equal, the resulting bit will be 0, otherwise 1.
The xor-function is the same as the eor function; both are synonymous; however they have each their own description, so you may check out the entry of xor for a slightly different view.
error — raise an error and terminate your program
error "Wrong, wrong, wrong !!"
Produces the same kind or error messages, that yabasic itself produces (e.g. in case of a syntax-error). The single argument is issued along with the current line-number.
input "Please enter a number between 1 and 10: " a
if (a<1 or a>10) error "Oh no ..."
This program is very harsh in checking the users input; instead of just asking again, the program terminates with an error, if the user enters something wrong.
The error message would look like this:
---Error in t.yab, line 2: Oh no ... ---Error: Program stopped due to an error
euler — another name for the constant 2.71828182864
foo=euler
eval() — compile and execute a single numeric expression
print eval("1+2")
eval accepts a string, which should be the text of a single numeric expression; it processes the expression and returns the result. All numeric functions and arithmetic operators of yabasic can be used as well as any variables known.
The string passed to eval is first compiled and then executed right away. The compilation happens just before the execution and may cause compilation errors, if you pass an invalid expression. eval might come handy, if you want to calculate an expression, that is not known at the start of your program, e.g. because it is read from the user; see the example below.
input "Please enter an aritmetic expression involving the variable x: " expr$
first = true
for x=0 to 100 step 0.01
result = eval(expr$)
if (first or result > maximum) maximum = result: xmaximum = x
first = false
next x
print "In the range 0 to 100, expression " + expr$ + " has its maximum of " + str$(maximum) + " at " + str$(xmaximum) + " (approximately)"
The example above reads an arithmetic expression from the user and steps through the range 0 … 100 to find its maximum. If the user types e.g. -(x-50)**2, the program would find a maximum of around zero (e.g. -1.90013e-24) at 50.
eval$() — compile and execute a single string-expression
print eval$("a$ + b$")
eval$ accepts a string, which should be the text of a single string-expression; it processes the expression and returns the result. All string-functions and string-operators of yabasic can be used as well as any variables known.
The string passed to eval$ is first compiled and then executed right away. The compilation happens right before the execution and may cause compilation errors, if you pass an invalid expression. See the example below for two interesting use-cases.
The example below allows to apply the quoting rules of yabasic to user-input:
input "Please enter a string with some excape-sequences (e.g. \\r,\\n,\\t): " a$
print eval$("\"" + a$ + "\"")
If the user types abc\ndef at the prompt, the text is echoed like this:
abc
def
The next example shows the subroutine evemex$ (for eval embedded expression) that allows to embed expressions into a string, simply by enclosing them with {{ and }}:
input "Please enter your name: " name$
print evemex$("Hello {{name$}}, your name has {{len(name$)}} characters.")
sub evemex$(evemex_str$)
local evemex_pos1, evemex_pos2, evemex_res$
evemex_pos1 = 1
evemex_pos2 = 1
evemex_res$ = ""
while (evemex_pos1 < len(evemex_str$))
if (mid$(evemex_str$, evemex_pos1, 2) = "{{") then
evemex_res$ = evemex_res$ + mid$(evemex_str$, evemex_pos2, evemex_pos1 - evemex_pos2)
evemex_pos1 = evemex_pos1 + 2
evemex_pos2 = evemex_pos1
while (evemex_pos2 < len(evemex_str$))
if (mid$(evemex_str$, evemex_pos2, 2) = "}}") then
rem
rem See the use of eval in the next line
rem
evemex_res$ = evemex_res$ + eval$("str$(" + mid$(evemex_str$, evemex_pos1, evemex_pos2 - evemex_pos1) + ")")
evemex_pos2 = evemex_pos2 + 2
evemex_pos1 = evemex_pos2
break
else
evemex_pos2 = evemex_pos2 + 1
endif
wend
else
evemex_pos1 = evemex_pos1 + 1
endif
wend
evemex_res$ = evemex_res$ + mid$(evemex_str$, evemex_pos2, evemex_pos1 - evemex_pos2 + 1)
return evemex_res$
end sub
If the user when prompted types Marc, he is greeted with Hello Marc, your name has 4 characters. The program uses eval$ only once, and it adds str$ around the embedded expression to ensure, that the result is always a string and can be concatenated with the other strings.
Please note, that the subroutine prefixes its local variables with evemex (for eval embedded expression) to avoid name clashes with any variable that might be used in expressions within the string passed.
execute() — execute a user defined subroutine, which must return a number
print execute("bar","arg1","arg2")
The execute-function is the counterpart of the execute$-function (please see there for some caveats). execute may be used to execute subroutines, which return a number.
execute$() — execute a user defined subroutine, which must return a string
print execute$("foo$","arg1","arg2")
execute$ can be used to execute a user defined subroutine, whose name is specified as a string expression.
This function allows to execute a subroutine, whose name is not known by the time you write your program. This might happen, if you want to execute a subroutine, which is compiled (using the compile command) as late as of execution of your program.
Note however, that the execute$-function is not the preferred method to execute a user defined subroutine; in almost all cases you should just execute a subroutine by writing down its name within your yabasic program (see the example below).
print execute$("foo$","Hello","world !")
sub foo$(a$,b$)
return a$+" "+b$
end sub
The example simply prints Hello world !, which is the return value of the user defined subroutine foo$. The same could be achieved by executing:
print foo$(a$,b$)
So this example does not really need the execute$-function; see compile for examples, that do.
exit — terminate your program
exit exit 1
Terminate your program and return any given value to the operating system. exit is similar to end, but it will terminate your program immediately, no matter what.
exp() — compute the exponential function of its single argument
foo=exp(bar)
This function computes e to the power of its argument, where e is the well known euler constant 2.71828182864.
The exp-function is the inverse of the log-function.
export — mark a function as globally visible
export sub foo(bar) … end sub
The export-statement is used within libraries to mark a user defined subroutine as visible outside the library wherein it is defined. Subroutines, which are not exported, must be qualified with the name of the library, e.g. foo.baz (where foo is the name of the library and baz the name of the subroutine); exported subroutines may be used without specifying the name of the library, e.g. bar.
Therefore export may only be useful within libraries.
The library foo.bar (which is listed below) defines two functions bar and baz, however only the function bar is exported and therefore visible even outside the library; baz is not exported and may only be used within the library foo.yab:
export sub bar()
print "Hello"
end sub
sub baz()
print "World"
end sub
Now within your main program cux.yab (which imports the library foo.yab); note that this program produces an error:
import foo print "Calling subroutine foo.bar (okay) ..." foo.bar() print "done." print "Calling subroutine bar (okay) ..." bar() print "done." print "Calling subroutine foo.baz (okay) ..." foo.baz() print "done." print "Calling subroutine baz (NOT okay) ..." baz() print "done."
The output when executing yabasic foo.yab is this:
Calling subroutine foo.bar (okay) ... Hello done. Calling subroutine bar (okay) ... Hello done. Calling subroutine foo.baz (okay) ... World done. Calling subroutine baz (NOT okay) ... ---Error in main.yab, line 16: can't find subroutine 'baz' ---Dump: sub baz() called in main.yab,16 ---Error: Program stopped due to an error
As the error message above shows, the subroutine baz must be qualified with the name of the library, if used outside the library, wherein it is defined (e.g. foo.baz). I.e. outside the library foo.yab you need to write foo.baz. baz alone would be an error.
The subroutine bar (without adding the name of the library) however may (and probably should) be used in any program, which imports the library foo.yab.
In some sense the set of exported subroutines constitutes the interface of a library.
circles, rectangles or triangles
for-loop
foreign_buffer_ and foreign_function_
false — a constant with the value of 0
okay=false
The constant false can be assigned to variables which later appear in conditions (e.g. within an if-statement.
false may also be written as FALSE or even FaLsE.
fi — another name for endif
if (…) … fi
fi marks the end of an if-statement and is exactly equivalent to endif, please see there for further information.
fill — draw a filled circles, rectangles or triangles
fill rectangle 10,10,90,90 fill circle 50,50,20 fill triangle 10,20,20,10,20,20
The keyword fill may be used within the circle, rectangle or triangle command and causes these shapes to be filled.
fill can be used in conjunction with and wherever the clear-clause may appear. Used alone, fill will fill the interior of the shape (circle, rectangle or triangle); together with clear the whole shape (including its interior) is erased.
floor() — compute the floor for its (float) argument
print floor(x)
The floor-function returns the largest integer number, that is smaller or equal than its argument. For positive numbers x, floor(x) is the same as int(x); for negaive numbers it can be different (see the example below).
for — starts a for-loop
for a=1 to 100 step 2 … next a
The for-loop lets its numerical variable (a in the synopsis) assume all values within the given range. The optional step-clause may specify a value (default: 1) by which the variable will be incremented (or decremented, if step is negative).
Any for-statement can be replaced by a set of ifs and gotos; as you may infer from the example below this is normally not feasible. However if you want to know in detail how the for-statement works, you should study this example, which presents a for-statement and an exactly equivalent series of ifs and gotos.
foreign_buffer_alloc$() — Create a new buffer for use in a foreign function call
handle$=foreign_buffer_alloc$(10)
foreign_buffer_alloc$() creates a new buffer of specified size (using the C-function malloc). This buffer can then be populated by foreign_buffer_set or foreign_buffer_set_buffer, passed to foreign_function_call and finally freed with foreign_buffer_free.
The special value of -1 can be passed to create the equivalent of a null-pointer in C: when your yabasic-program passes such a buffer to an external function, it is replaced by a null-pointer.
foreign_buffer_dump$() — return the content of a buffer as a hex-encoded string
print foreign_buffer_dump(handle$)
foreign_buffer_dump$() is mostly used during development of your yabasic program and helps to investigate the content of a buffer; this can be helpful to find out, how a structure for a foreign function call is aggregated. To actually retrieve elements from the structure rather use foreign_buffer_get.
foreign_buffer_free — free a foreign buffer
foreign_buffer_free handle$
foreign_buffer_free() expects a handle for a buffer and frees this buffer (using the C-function free), i.e. gives this memory area back to the operating system. Any subsequent attempt to access part of this buffer (e.g. via foreign_buffer_get) will probably lead to an error (as will a second call to foreign_buffer_free()). The handle-argument must have been returned previously by foreign_buffer_alloc or foreign_function_call.
foreign_buffer_get() — extract a number from a foreign buffer
print foreign_buffer_get(handle$,10,"int")
foreign_buffer_get() retrieves a simple type from a buffer, that is assumed to contain a structure (see the overview-section for the necessary background). For this it needs three arguments:
A handle to a buffer, that has been previously filled, e.g. by a foreign function call.
An offset, counted in bytes from the start of the buffer, which specifies where the value can be found within the structure.
A string, specifying the type of the value that should be retrieved, which for this function is always an integer type like "int", "short" or "long".
Correct usage of this function requires an good understanding of the respective structure contained within the buffer.
The overview-section on foreign functions, list of related functions and commands, the neighbouring functions for retrieving other values from the buffer.
foreign_buffer_get$() — extract a string from a foreign buffer
print foreign_buffer_get$(handle$,0,12)
foreign_buffer_get$() retrieves a string from a foreign buffer; its areguments are
A handle to a buffer, that has been previously filled, e.g. by a foreign function call.
An offset within this buffer, where the string starts. In the common case, where the buffer can be assumed to contain a string only, this offset should be 0.
The maximum length of the expected string. This is a value not necessarily known but if the string is null-terminated (as usual) you may just specify a much larger number here.
Correct usage of this function requires an good understanding of the respective structure contained within the buffer.
foreign_buffer_get_buffer() — take a buffer and construct a handle to a second buffer from its content
handle2$ = foreign_buffer_get_buffer(handle$,8)
foreign_buffer_get_buffer() should be used, if a buffer (i.e. the contained structure) is known to contain a pointer to a string or another structure. foreign_buffer_get_buffer() then reads this pointer and transforms it into a handle, that can then be used by other functions from the foreign_buffer_get-family. The two arguments are:
A handle to a buffer, that has been previously filled, e.g. by a foreign function call.
An offset within the buffer to the start of the buffer. A (third) length-argument is not required, because typically all pointers on a platform have the same length.
See the libcurl-example in the overview-section for an example.
foreign_buffer_set — store a given value within a buffer
foreign_buffer_set handle$,4,"Hello World" foreign_buffer_set handle$,6,"long",42
foreign_buffer_set can be used to populate a structure within a foreign buffer. It accepts strings (first line in synopsis) and numbers (second line in synopsis) and stores them at the given offset. The arguments are:
A handle to a buffer, that might have been just allocated or been returned from a foreign function call.
An offset, specifying the first byte where the given data will be stored.
The third argument: If you want to store a string, specify it just here; if you want to store a number, specify its type (e.g. int).
A fourth argument is only needed, when you want to store a number; this number needs then to be given here.
foreign_buffer_set_buffer — store a pointer to one buffer within another buffer
foreign_buffer_set handle1$,16,handle2$
foreign_buffer_set_buffer stores a pointer (as in C) to a buffer within another buffer. It accepts a handle to a buffer (handle2$ in the synopsis) and stores it as a pointer at the given offset within the buffer given first (handle1$). The arguments are:
A handle to a buffer, that might have been just allocated or been returned from a foreign function call.
An offset, specifying the first byte where the pointer to the given buffer will be stored.
A handle to a buffer whose address (pointer) will be stored within the first buffer.
foreign_buffer_size() — return the size of the foreign buffer
size = foreign_buffer_size(handle$)
foreign_function_call() — call a function (returning a number) from a non-yabasic library or dll
print foreign_function_call("libtimestwo","int","timestwo","int",3)
foreign_function_call calls a function from an external library.
In general, this feature is mostly useful, if you have such a library written or aquired. If you have an external command, that can be called interactively (i.e. from the commandline), you might try the system-function.
Please see the overview-section on foreign functions for overview, background and more examples. For details on functionality and arguments see below.
The example uses the foreign_function_call to invoke the cos-function from the standard C-library (libm.so.6 under Unix or msvcrt.dll under Windows).
if peek$("os") = "unix" then
lib$ = "libm.so.6"
else
lib$ = "msvcrt.dll"
fi
print foreign_function_call(lib$,"double","cos","double",2)
The foreign_function_call-function accepts a variable number of arguments; 3 at minimum, 5 in the example above:
A string, containing the name of the library, e.g. "libm.so.6".
A string describing the type, that the function (specified with the next argument) returns (in the example: "double"). See below for a list of all such types.
The name of the function, that should be called (in the example above: "cos")
If the external function does not require arguments itself, the three arguments above are everything needed for foreign_function_call. However (as for cos), if the external function itself requires arguments, than for each of its arguments, two more arguments are needed foreign_function_call:
A string describing the type of the parameter to the external function (in the example: "double"). See the overview-section on foreign functions for a list of all such types.
A value, that can be converted to the specified type (in the example: 2).
With all these arguments specified, yabasic will call the foreign function (in the example: cos) and return its result; this process can be influenced by specifying options (see below).
Options can be appended in any number after the string "options", e.g. like:
foreign_function_call(lib$,"double","cos","double",2,"options","error")
Each option can be preceded with the string no_ to invert its meaning. As given below (i.e. with or without no_) the values represent the respective default.
error
In case of errors (e.g. if a library cannot be found), should the function report them actively (which terminates your yabasic-program) ? Or should the error silently stored away for later retrieval by peek("last_foreign_function_call_okay") and peek$("last_foreign_function_call_error_text") ?
no_copy_string_result
If the foreign function returns a string-value (like strstr), it should be invoked using foreign_function_call$, which returns a string. Now, depending on the foreign function invoked, it might be necessary to make a copy of its result before returning it to yabasic. In the case of strstr this is needed, because it returns just a pointer to part of its input string which will yabasic happily free later on, probably leading to a segfault after.
no_unload_library
Normally, after making a call to a foreign function, the named library is kept in memory for further use (see background). However, sometimes you might want to dismiss the library right after the call; then you may specify this option.
foreign_function_call$() — call a function (returning a string or a buffer) from a non-yabasic library or dll
a$=foreign_function_call$("libupper","string","toupper","string","hello world")
This function calls a function from an external library, just like foreign_function_call (which see for most of the description). The only difference is that foreign_function_call$ should be used when the foreign function returns a string or a structure (which itself is contained in a buffer, which is represented by a handle, which is a string).
The arguments are just the same as in foreign_function_call, only the second argument ("string" in the example above) can only be "string" or "buffer" in accord to the nature of foreign_function_call$, which itself must return a string.
Among the options described at foreign_function_call, the option "copy_string_result" can really only be applied here.
foreign_function_size() — return the size of one of the types available for foreign function calls
offset=foreign_function_size("short")
The function returns the size of any of the types available for calls to foreign functions (see the overview section for a complete list). This is useful when calculating offsets needed for foreign_buffer_set or foreign_buffer_get.
frnbf_ and frnfn_ — Abbreviations for foreign_buffer_ and foreign_function_
print frnfn_size("short")
frac() — return the fractional part of its numeric argument
x=frac(y)
The frac-function takes its argument, removes all the digits to the left of the comma and just returns the digits right of the comma, i.e. the fractional part.
Refer to the example to learn how to rewrite frac by employing the int-function (which is not suggested anyway).
for a=1 to 10
print frac(sqr(a))
print sqr(a)-int(sqr(a))
next a
The example prints the fractional part of the square root of the numbers between 1 and 10. Each result is computed (and printed) twice: Once by employing the frac-function and once by employing the int-function.
getbit$() — return a string representing the bit pattern of a rectangle within the graphic window
a$=getbit$(10,10,20,20) a$=getbit$(10,10 to 20,20)
The function getbit returns a string, which contains the encoded bit-pattern of a rectangle within graphic window; the four arguments specify two opposite corners of the rectangle. The string returned might later be fed to the putbit-command.
The getbit$-function might be used for simple animations (as in the example below).
getscreen$() — returns a string representing a rectangular section of the text terminal
a$=getscreen$(2,2,20,20)
The getscreen$ function returns a string representing the area of the screen as specified by its four arguments (which specify two opposite corners). I.e. everything you have printed within this rectangle will be encoded in the string returned (including any colour-information).
Like most other commands dealing with advanced text output, getscreen$ requires, that you have called clear screen before.
clear screen
for a=1 to 1000:
print color("red") "1";
print color("green") "2";
print color("blue") "3";
next a
screen$=getscreen$(10,10,40,10)
print at(10,10) " Please Press 'y' or 'n' ! "
a$=inkey$
putscreen screen$,10,10
This program fills the screen with colored digits and afterwards asks the user for a choice ( Please press 'y' or 'n' ! ). Afterwards the area of the screen, which has been overwritten by the question will be restored with its previous contents, whhch had been saved via getscreen$.
glob() — check if a string matches a simple pattern
if (glob(string$,pattern$)) …
The glob-function takes two arguments, a string and a (glob-) pattern, and checks if the string matches the pattern. However glob does not employ the powerful rules of regular expressions; rather it has only two special characters: * (which matches any number (even zero) of characters) and ? (which matches exactly a single character).
for a=1 to 10
read string$,pattern$
if (glob(string$,pattern$)) then
print string$," matches ",pattern$
else
print string$," does not match ",pattern$
endif
next a
data "abc","a*"
data "abc","a?"
data "abc","a??"
data "abc","*b*"
data "abc","*"
data "abc","???"
data "abc","?"
data "abc","*c"
data "abc","A*"
data "abc","????"
This program checks the string abc against various patterns and prints the result. The output is:
abc matches a* abc does not match a? abc matches a?? abc matches *b* abc matches * abc matches ??? abc does not match ? abc matches *c abc does not match A* abc does not match ????
gosub — continue execution at another point within your program (and return later)
gosub foo … label foo … return
gosub remembers the current position within your program and then passes the flow of execution to another point (which is normally marked with a label). Later, when a return-statement is encountered, the execution is resumed at the previous location.
gosub is the traditional command for calling code, which needs to be executed from various places within your program. However, with subroutines yabasic offers a much more flexible way to achieve this (and more). Therefore gosub must to be considered obsolete.
goto — continue execution at another point within your program (and never come back)
goto foo … label foo
The goto-statement passes the flow of execution to another point within your program (which is normally marked with a label).
goto is normally considered obsolete and harmful, however in yabasic it may be put to the good use of leaving loops (e.g. while or for) prematurely. Note however, that subroutines may not be left with the goto-statement.
hex$() — convert a number into hexadecimal
print hex$(foo)
The hex$-function converts a number into a string with its hexadecimal representation. hex$ is the inverse of the dec-function.
if — evaluate a condition and execute statements or not, depending on the result
if (…) then … endif if (…) … if (…) then … else … endif if (…) then … elsif (…) … elsif (…) then … else … endif
The if-statement is used to evaluate a conditions and take actions accordingly. (As an aside, please note that there is no real difference between conditions and expressions.)
There are two major forms of the if-statement:
The one-line-form without the keyword then:
if (…) …
This form evaluates the condition and if the result is true executes all commands (separated by colons) upt to the end of the line. There is neither an endif keyword nor an else-branch.
The multi-line-form with the keyword then:
if (…) then … elsif (…) … else … endif
(where elsif and else are optional, whereas endif is not.
According to the requirements of your program, you may specify:
elsif(…), which specifies a condition, that will be evaluated only if the condition(s) within if or any preceding elsif did not match.
else, which introduces a sequence of commands, that will be executed, if none of the conditions above did match.
endif is required and ends the if-statement.
input "Please enter a number between 1 and 4: " a
if (a<=1 or a>=4) error "Wrong, wrong !"
if (a=1) then
print "one"
elsif (a=2)
print "two"
elsif (a=3)
print "three"
else
print "four"
endif
The input-number between 1 and 4 is simply echoed as text (one, two, …). The example demonstrates both forms (short and long) of the if-statement (Note however, that the same thing can be done, probably somewhat more elegant, with the switch-statement).
import — import a library
import foo
The import-statement imports a library. It expects a single argument, which must be the name of a library (without the trailing .yab). This library will then be read and parsed and its subroutines (and variables) will be made available within the importing program. Most of the time this will be the main program, but libraries my also import and use other libraries.
Libraries will first be searched in three locations in order:
The current directory, i.e. the directory from which you have invoked yabasic)
The directory, where your main program lives. This can be different from the first directory, if you specify a path for your main program, e.g. like yabasic foo/bar.yab.
Finally, libraries are searched within a special directory, whose exact location depends on your system or options when invoking yabasic. Typical values would be /usr/lib under Unix or C:\yabasic\lib under Windows. Invoking yabasic --help will show the correct directory. The location of this directory may be changed with the option --librarypath (see options).
Lets say you have a yabasic-program foo.yab, which imports a library lib.yab. foo.yab; this would read:
import lib
rem This works
lib.x(0)
rem This works too
x(1)
rem And this
lib.y(2)
rem But this not !
y(3)
Now the library lib.yab reads:
rem Make the subroutine x easily available outside this library export sub x(a) print a return end sub rem sub y must be referenced by its full name rem outside this library sub y(a) print a return end sub
This program produces an error:
0 1 2 ---Error in foo.yab, line 13: can't find subroutine 'y' ---Dump: sub y() called in foo.yab,13 ---Error: Program stopped due to an error
As you may see from the error message, yabasic is unable to find the subroutine y without specifying the name of the library (i.e. lib.y). The reason for this is, that y, other than x, is not exported from the library lib.yab (using the export-statement).
inkey$ — wait, until a key is pressed
clear screen foo$=inkey$ inkey$ foo$=inkey$(bar) inkey$(bar)
The inkeys$-function waits, until the user presses a key on the keyboard or a button of his mouse, and returns this very key. An optional argument specifies the number of seconds to wait; if omitted, inkey$ will wait indefinitely.
inkey$ may only be used, if clear screen has been called at least once.
For normal keys, yabasic simply returns the key, e.g. a, 1 or !. For function keys you will get f1, f2 and so on. Other special keys will return these strings respectively: enter, backspace, del, esc, scrnup (for screen up), scrndown and tab. Modifier keys (e.g. ctrl, alt or shift) by themselves can not be detected (e.g. if you simultaneously press shift and 'a', inkey$ will return the letter 'A' instead of 'a' of course).
If a graphical window has been opened (via open window) any mouseclick within this window will be returned by inkey$ too. The string returned (e.g. MB1d+0:0028,0061, MB2u+0:0028,0061 or MB1d+1:0028,0061) is constructed as follows:
Every string associated with a mouseclick will start with the fixed string MB
The next digit (1, 2 or 3) specifies the mousebutton pressed.
A single letter, d or u, specifies, if the mousebutton has been pressed or released: d stands for down, i.e. the mousebutton has been pressed; u means up, i.e. the mousebutton has been released.
The plus-sign ('+'), which follows is always fixed.
The next digit (in the range 0 to 7) encodes the modifier keys pressed, where 1 stands for shift, 2 stands for alt and 4 stands for ctrl.
The next four digits (e.g. 0028) contain the x-position, where the mousebutton has been pressed.
The comma to follow is always fixed.
The last four digits (e.g. 0061) contain the y-position, where the mousebutton has been pressed.
All those fields are of fixed length, so you may use functions like mid$ to extract certain fields. However, note that with mousex, mousey, mouseb and mousemod there are specialized functions to return detailed information about the mouseclick. Finally it should be noted, that inkey$ will only register mouseclicks within the graphic-window; mouseclicks in the text-window cannot be detected.
inkey$ accepts an optional argument, specifying a timeout in seconds; if no key has been pressed within this span of time, an empty string is returned. If the timeout-argument is omitted, inkey$ will wait for ever.
input — read input from the user (or from a file) and assign it to a variable
input a input a,b,c input a$ input "Hello" a input #1 a$
input reads the new contents of one or many (numeric- or string-) variables, either from the keyboard (i.e. from you) or from a file. An optional first string-argument specifies a prompt, which will be issued before reading any contents.
If you want to read from an open file, you need to specify a hash ('#'), followed by the number, under which the file has been opened.
Note, that the input is split at spaces, i.e. if you enter a whole line consisting of many space-separated word, the first input-statement will only return the first word; the other words will only be returned on subsequent calls to input; the same applies, if a single input reads multiple variables: The first variable gets only the first word, the second one the second word, and so on. If you don't like this behaviour, you may use line input, which returns a whole line (including embedded spaces) at once.
input "Please enter the name of a file to read: " a$
open 1,a$
while !eof(1)
input #1 b$
print b$
wend
If this program is stored within a file test.yab and you enter this name when prompted for a file to read, you will see this output:
Please enter the name of a file to read: t.yab input "Please enter the name of a file to read: " a$ open 1,a$ while !eof(1) input #1 b$ print b$ wend
instr() — searches its second argument within the first; returns its position if found
print instr(a$,b$) if (instr(a$,b$)) … pos=instr(a$,b$,x)
The instr-functions requires two string arguments and searches the second argument within the first. If the second argument can be found within the first, the position is returned (counting from one). If it can not be found, the instr-function returns 0; this makes this function usable within the condition of an if-statement (see the example below).
If you supply a third, numeric argument to the instr-function, it will be used as a starting point for the search. Therefore instr("abcdeabcdeabcde","e",8) will return 10, because the search for an "e" starts at position 8 and finds the "e" at position 10 (and not the one at position 5).
int() — return the integer part of its single numeric argument
print int(a)
The int-function returns only the digits before the comma; int(2.5) returns 2 and int(-2.3) returns -2.
goto, gosub or restore
label — mark a specific location within your program for goto, gosub or restore
label foo … goto foo
The label-command can be used to give a name to a specific location within your program. Such a position might be referred from one of three commands: goto, gosub and restore.
You may use labels safely within libraries, because a label (e.g. foo) does not collide with a label with the same name within the main program or within another library; yabasic will not mix them up.
As an aside, please note, that line numbers are a special (however deprecated) case of labels; see the second example below.
left$() — return (or change) left end of a string
print left$(a$,2) left$(b$,3)="foobar"
The left$-function accepts two arguments (a string and a number) and returns the part from the left end of the string, whose length is specified by its second argument. Loosely spoken, it simply returns the requested number of chars from the left end of the given string.
Note, that the left$-function can be assigned to, i.e. it may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the left$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.
input "Please answer yes or no: " a$
l=len(a$):a$=lower$(a$):print "Your answer is ";
if (left$("yes",l)=a$ and l>=1) then
print "yes"
elsif (left$("no",l)=a$ and l>=1) then
print "no"
else
print "?"
endif
This example asks a simple yes/no question and goes some way to accept even incomplete input, while still being able to reject invalid input.
This second example demonstrates the capability to assign to the left$-function.
a$="Heiho World !" print a$ left$(a$,5)="Hello" print a$
len() — return the length of a string
x=len(a$)
line — draw a line
open window 100,100 line 0,0,100,100 line 0,0 to 100,100 new curve line 100,100 line to 100,100 open window 100,100 clear line 0,0,100,100 clear line 0,0 to 100,100 new curve clear line 100,100 clear line to 100,100
The line-command draws a line. Simple as this is, the line-command has a large variety of forms as they are listed in the synopsis above. Lets look at them a little closer:
A line has a starting and an end point; therefore the line-command (normally) needs four numbers as arguments, representing these two points. This is the first form appearing within the synopsis.
You may separate the two points with either ',' or to, which accounts for the second form of the line-command.
The line-command may be used to draw a connected sequence of lines with a sequence of commands like line x,y; Each command will draw a line from the point where the last line-command left off, to the point specified in the arguments. Note, that you need to use the command new curve before you may issue such a line-command. See the example below.
You may insert the word to for beauty: line to x,y, which does exactly the same as line x,y
Finally, you may choose not to draw, but to erase the lines; this can be done by prepending the phrase clear. This account for all the other forms of the line-command.
open window 200,200
line 10,10 to 10,190
line 10,190 to 190,190
new curve
for a=0 to 360
line to 10+a*180/360,100+60*sin(a*pi/180)
next a
This example draws a sine-curve (with an offset in x- and y-direction). Note, that the first line-command after new curve does not draw anything. Only the coordinates will be stored. The second iteration of the loop then uses these coordinates as a starting point for the first line.
line input — read in a whole line of text and assign it to a variable
line input a line input a$ line input "Hello" a line input #1 a$
In most respects line input is like the input-command: It reads the new contents of a variable, either from keyboard or from a file. However, line input always reads a complete line and assigns it to its variable. line input does not stop reading at spaces and is therefore the best way to read in a string which might contain whitespace. Note, that the final newline is stripped of.
local — mark a variable as local to a subroutine
sub foo() local a,b,c$,d(10),e$(5,5) … end sub
The local-command can (and should be) used to mark a variable (or array) as local to the containing subroutine. This means, that a local variable in your subroutine is totally different from a variable with the same name within your main program. Variables which are known everywhere within your program are called global in contrast.
Declaring variables within the subroutine as local helps to avoid hard to find bugs; therefore local variables should be used whenever possible.
Note, that the parameters of your subroutines are always local.
As you may see from the example, local arrays may be created without using the keyword dim (which is required only for global arrays).
a=1
b=1
print a,b
foo()
print a,b
sub foo()
local a
a=2
b=2
end sub
This example demonstrates the difference between local and global variables; it produces this output:
1 1 1 2
As you may see, the content of the global variable a is unchanged after the subroutine foo; this is because the assignment a=2 within the subroutine affects the local variable a only and not the global one. However, the variable b is never declared local and therefore the subroutine changes the global variable, which is reflected in the output of the second print-statement.
log() — compute the natural logarithm
a=log(x) a=log(x,base)
The log-function computes the logarithm of its first argument. The optional second argument gives the base for the logarithm; if this second argument is omitted, the euler-constant 2.71828… will be taken as the base.
loop — marks the end of an infinite loop
do … loop
The loop-command marks the ends of a loop (which is started by do), wherein all statements within the loop are repeated forever. In this respect the do loop-loop is infinite, however, you may leave it anytime via break or goto.
lower$() — convert a string to lower case
l$=lower$(a$)
ltrim$() — trim spaces at the left end of a string
a$=ltrim$(b$)
The ltrim$-function removes all whitespace from the left end of a string and returns the result.
input "Please answer 'yes' or 'no' : " a$
a$=lower$(ltrim$(rtrim$(a$)))
if (len(a$)>0 and a$=left$("yes",len(a$))) then
print "Yes ..."
else
print "No ..."
endif
This example prompts for an answer and removes any spaces, which might precede the input; therefore it is even prepared for the (albeit somewhat pathological case, that the user first hits space before entering his answer.
inkey$
max() — return the larger of its two arguments
print max(a,b)
dim m(10)
for a=1 to 1000
m=0
For b=1 to 10
m=max(m,ran(10))
next b
m(m)=m(m)+1
next a
for a=1 to 9
print a,": ",m(a)
next a
Within the inner for-loop (the one with the loop-variable b), the example computes the maximum of 10 random numbers. The outer loop (with the loop variable a) now repeats this process 1000 times and counts, how often each maximum appears. The last loop finally reports the result.
Now, the interesting question would be, which will be approached, when we increase the number of iterations from thousand to infinity. Well, maybe someone could just tell me :-)
mid$() — return (or change) characters from within a string
print mid$(a$,2,1) print mid$(a$,2) mid$(a$,5,3)="foo" mid$(a$,5)="foo"
The mid$-function requires three arguments: a string and two numbers, where the first number specifies a position within the string and the second one gives the number of characters to be returned; if you omit the third argument, the mid$-function returns all characters up to the end of the string.
Note, that you may assign to the mid$-function, i.e. mid$ may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the mid$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.
input "Please enter a string: " a$
for a=1 to len(a$)
if (instr("aeiou",lower$(mid$(a$,a,1)))) mid$(a$,a,1)="e"
next a
print "When you turn everything to lower case and"
print "replace every vowel with 'e', your input reads:"
print
print a$
This example transforms the input string a bit, using the mid$-function to retrieve a character from within the string as well as to change it.
min() — return the smaller of its two arguments
print min(a,b)
mod — compute the remainder of a division
print mod(a,b)
The mod-function divides its two arguments and computes the remainder. Note, that a/b-int(a/b) and mod(a,b) are always equal.
clear screen
print at(10,10) "Please wait ";
p$="-\|/"
for a=1 to 100
rem ... do something lengthy here, or simply sleep :-)
pause(1)
print at(22,10) mid$(p$,1+mod(a,4))
next a
This example executes some time consuming action within a loop (in fact, it simply sleeps) and gives the user some indication of progress by displaying a rotating bar (that's where the mod-function comes into play).
mouseb — extract the state of the mousebuttons from a string returned by inkey$
inkey$ print mouseb() print mouseb a$=inkey$ print mouseb(a$)
The mouseb-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function. If a mousebutton has been pressed, the mouseb-function returns the number (1,2 or 3) of the mousebutton, when it is pressed and returns its negative (-1,-2 or -3), when it is released.
The mouseb-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mouseb is called without any arguments, it returns the values from the last call to inkey$, which are stored implicitly and internally by yabasic.
Note however, that the value returned by the mouseb-function does not reflect the current state of the mousebuttons. It rather extracts the information from the string passed as an argument (or from the last call to the inkey$-function, if no argument is passed). So the value returned by mouseb reflects the state of the mousebuttons at the time the inkey$-function has been called; as opposed to the time the mouseb-function is called.
open window 200,200
clear screen
print "Please draw lines; press (and keep it pressed)"
print "the left mousebutton for the starting point,"
print "release it for the end-point."
do
if (mouseb(release$)=1) press$=release$
release$=inkey$
if (mouseb(release$)=-1) then
line mousex(press$),mousey(press$) to mousex(release$),mousey(release$)
endif
loop
This is a maybe the most simplistic line-drawing program possible, catching presses as well as releases of the first mousebutton.
mousemod — return the state of the modifier keys during a mouseclick
inkey$ print mousemod() print mousemod a$=inkey$ print mousemod(a$)
The mousemod-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function if a mousebutton has been pressed. It returns the state of the keyboard modifiers (shift, ctrl or alt): If the shift-key is pressed, mousemod returns 1, for the alt-key 2 and for the ctrl-key 4. If more than one key is pressed, the sum of these values is returned, e.g. mousemod returns 5, if shift and ctrl are pressed simultaneously.
The mousemod-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousemod is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).
Please see also the Note within the mouseb-function.
open window 200,200
clear screen
do
a$=inkey$
if (left$(a$,2)="MB") then
x=mousex(a$)
y=mousey(a$)
if (mousemod(a$)=0) then
circle x,y,20
else
fill circle x,y,20
endif
endif
loop
This program draws a circle, whenever a mousebutton is pressed; the circles are filled, when any modifier is pressed, and empty if not.
mousex — return the x-position of a mouseclick
inkey$ print mousex() print mousex a$=inkey$ print mousex(a$)
The mousex-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function; It returns the x-position of the mouse as encoded within its argument.
The mousex-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousex is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).
Please see also the Note within the mouseb-function.
mousey — return the y-position of a mouseclick
inkey$ print mousey() print mousey a$=inkey$ print mousey(a$)
The mousey-function is a helper function for decoding part of the (rather complicated) strings, which are returned by the inkey$-function. mousey returns the y-position of the mouse as encoded within its argument.
The mousey-function accepts zero or one arguments. A single argument should be a string returned by the inkey$-function; if mousey is called without any arguments, it returns the values from the last call to inkey$ (which are stored implicitly and internally by yabasic).
Please see also the Note within the mouseb-function.
new curve — start a new curve, that will be drawn with the line-command
new curve line to x,y
The new curve-function starts a new sequence of lines, that will be drawn by repeated line to-commands.
open window 200,200
ellipse(100,50,30,60)
ellipse(150,100,60,30)
sub ellipse(x,y,xr,yr)
new curve
for a=0 to 2*pi step 0.2
line to x+xr*cos(a),y+yr*sin(a)
next a
close curve
end sub
This example defines a subroutine ellipse that draws an ellipse. Within this subroutine, the ellipse is drawn as a sequence of lines started with the new curve command and closed with close curve.
next — mark the end of a for loop
for a=1 to 10 next a
The next-keyword marks the end of a for-loop. All statements up to the next-keyword will be repeated as specified with the for-clause. Note, that the name of the variable is optional; so instead of next a you may write next.
not — negate a logical expression; can be written as !
if not a<b then … bad=!okay
The keyword not (or ! for short) is mostly used within conditions (e.g. within if- or while-statements). There it is employed to negate the condition or expression (i.e. turn TRUE into FALSE and vice versa)
However not can be used within arithmetic calculations too., simply because there is no difference between arithmetic and logical expressions.
numparams — return the number of parameters, that have been passed to a subroutine
sub foo(a,b,c) if (numparams=1) … … end sub
Within a subroutine the local variable numparam or numparams contains the number of parameters, that have been passed to the subroutine. This information can be useful, because the subroutine may have been called with fewer parameters than actually declared. The number of values that actually have been passed while calling the subroutine, can be found in numparams.
Note, that arguments which are used in the definition of a subroutine but are left out during a call to it (thereby reducing the value of numparams) receive a value of 0 or "" (empty string) respectively.
a$="123456789"
print part$(a$,4)
print part$(a$,3,7)
sub part$(a$,f,t)
if (numparams=2) then
return mid$(a$,f)
else
return mid$(a$,f,t-f+1)
end if
end sub
When you run this example, it will print 456789 and 34567. Take a look at the subroutine part$, which returns part of the string which has been passed as an argument. If (besides the string) two numbers are passed, they define the starting and end position of the substring, that will be returned. However, if only one number is passed, the rest of the string, starting from this position will be returned. Each of these cases is recognized with the help of the numparams variable.
gosub-targets
goto-targets
on goto — jump to one of multiple gosub-targets
on a gosub foo,bar,baz … label foo … return label bar … return label baz … return
The on gosub statement uses its numeric argument (the one between on and gosub) to select an element from the list of labels, which follows after the gosub-keyword: If the number is 1, the program does a gosub to the first label; if the number is 2, to the second and, so on. if the number is zero or less, the program continues at the position of the first label; if the number is larger than the total count of labels, the execution continues at the position of the last label; i.e. the first and last label in the list constitute some kind of fallback-slot.
Note, that the on gosub-command can no longer be considered state of the art; people (not me !) may even start to mock you, if you use it.
do
print "Please enter a number between 1 and 3: "
print
input "Your choice " a
on a gosub bad,one,two,three,bad
loop
label bad
print "No. Please between 1 and 3"
return
label one
print "one"
return
label two
print "two"
return
label three
print "three"
return
Note, how invalid input (a number less than 1, or larger than 3) is automatically detected.
on goto — jump to one of many goto-targets
on a goto foo,bar,baz … label foo … label bar … label baz …
The on goto statement uses its numeric argument (the one between on and goto to select an element from the list of labels, which follows after the goto-keyword: If the number is 1, the execution continues at the first label; if the number is 2, at the second, and so on. if the number is zero or less, the program continues at the position of the first label; if the number is larger than the total count of labels, the execution continues at the position of the last label; i.e. the first and last label in the list constitute some kind of fallback-slot.
Note, that (unlike the goto-command) the on goto-command can no longer be considered state of the art; people may (not me !) even start to mock you, if you use it.
label over
print "Please Select one of these choices: "
print
print " 1 -- show time"
print " 2 -- show date"
print " 3 -- exit"
print
input "Your choice " a
on a goto over,show_time,show_date,terminate,over
label show_time
print time$()
goto over
label show_date
print date$()
goto over
label terminate
exit
Note, how invalid input (a number less than 1, or larger than 3) is automatically detected; in such a case the question is simply issued again.
on interrupt — change reaction on keyboard interrupts
on interrupt break … on interrupt continue
With the on interrupt-command you may change the way, how yabasic reacts on a keyboard interrupt; it comes in two variants: on interrupt break and on interrupt continue. A keyboard interrupt is produced, if you press ctrl-C on your keyboard; normally (and certainly after you have called on interrupt break), yabasic will terminate with an error message. However after the command on interrupt continue yabasic ignores any keyboard interrupt. This may be useful, if you do not want your program being interruptible during certain critical operations (e.g. updating of files).
print "Please stand by while writing a file with random data ..."
on interrupt continue
open "random.data" for writing as #1
for a=1 to 100
print #1 ran(100)
print a," percent done."
sleep 1
next a
close #1
on interrupt continue
This program writes a file with 100 random numbers. The on interrupt continue command insures, that the program will not be terminated on a keyboard interrupt and the file will be written entirely in any case. The sleep-command just stretches the process artificially to give you a chance to try a ctrl-C.
open — open a file
open a,"file","r"
open #a,"file","w"
open #a,printer
open "file" for reading as a
open "file" for writing as #a
a=open("file")
a=open("file","r")
if (open(a,"file")) …
if (open(a,"file","w")) …
The open-command opens a file for reading or writing or a printer for printing text. open comes in a wide variety of ways; it requires these arguments:
In the synopsis this is a or #a. In yabasic each file is associated with a number between 1 and a maximum value, which depends on the operating system. For historical reasons the filenumber can be preceded by a hash ('#'). Note, that specifying a filenumber is optional; if it is omitted, the open-function will return a filenumber, which should then be stored in a variable for later reference. This filenumber can be a simple number or an arbitrary complex arithmetic expression, in which case braces might be necessary to save yabasic from getting confused.
In the synopsis above this is "file". This string specifies the name of the file to open (note the important caveat on specifying these filenames).
In the synopsis this is "r", "w", for reading or for writing. This string or clause specifies the mode in which the file is opened; it may be one of:
Open the file for reading (may also be written as for reading). If the file does not exist, the command will fail. This mode is the default, i.e. if no mode is specified with the open-command, the file will be opened with this mode.
Open the file for writing (may also be written as for writing). If the file does not exist, it will be created.
Open the file for appending, i.e. what you write to the file will be appended after its initial contents. If the file does not exist, it will be created.
This letter may not appear alone, but may be combined with the other letters (e.g. "rb") to open a file in binary mode (as opposed to text mode).
As you may see from the synopsis, the open-command may either be called as a command (without braces) or as a function (with braces). If called as a function, it will return the filenumber or zero if the operation fails. Therefore the open-function may be used within the condition of an if-statement.
If the open-command fails, you may use peek("error") to retrieve the exact nature of the error.
Furthermore note, that there is another, somewhat separate usage of the open-command; if you specify the bareword printer instead of a filename, the command opens a printer for printing text. Every text (and only text) you print to this file will appear on your printer. Note, that this is very different from printing graphics, as can be done with open printer.
open printer — open printer for printing graphics
open printer open printer "file"
The open printer-command opens a printer for printing graphics. The command requires, that a graphic window has been opened before. Everything that is drawn into this window will then be sent to the printer too.
A new piece of paper may be started with the clear window-command; the final (or only) page will appear after the close printer-command.
Note, that you may specify a filename with open printer; in that case the printout will be sent to a filename instead to a printer. Your program or the user will be responsible for sending this file to the printer afterwards.
If you use yabasic under Unix, you will need a postscript printer (because yabasic produces postscript output). Alternatively you may use ghostscript to transform the postscript file into a form suitable for your printer; but that is beyond the responsibility of yabasic.
open window — open a graphic window
open window x,y open window x,y,"font"
The open window-command opens a window of the specified size. Only one window can be opened at any given moment of time.
An optional third argument specifies a font to be used for any text within the window. It can however be changed with any subsequent text-command.
or — logical or, used in conditions
if a or b … while a or b …
or() — arithmetic or, used for bit-operations
x=or(a,b)
Used to compute the bitwise or of both its argument. Both arguments are treated as binary numbers (i.e. a sequence of digits 0 and 1); a bit of the resulting value will then be 1, if any of its arguments has 1 at this position in their binary representation.
Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to or.
3.14159
print color
pause — pause, sleep, wait for the specified number of seconds
pause 5
The pause-command has many different names: You may write pause, sleep or wait interchangeably; whatever you write, yabasic will always do exactly the same.
The pause-command will simply wait for the specified number of seconds. This may be a fractional number, so you may well wait less than a second. However, if you try to pause for a smaller and smaller interval (e.g. 0.1 seconds, 0.01 seconds, 0.001 seconds and so on) you will find that at some point yabasic will not wait at all. The minimal interval that can be waited depends on the system (Unix, Windows) you are using.
The pause-command cannot be interrupted. However, sometimes you may want the wait to be interruptible by simply pressing a key on the keyboard. In such cases you should consider using the inkey$-function, with a number of seconds as an argument).
deg=0
do
maxx=44+40*sin(deg)
for x=1 to maxx
print "*";
next x
pause 0.1+(maxx*maxx/(4*84*84))
print
deg=deg+0.1
loop
This example draws a sine-curve; due to the pause-statement the speed of drawing varies in the same way as the speed of a ball might vary, if it would roll along this curve under the influence of gravity.
peek — retrieve various internal information
print peek("foo")
a=peek(#1)
The peek-function has many different and mostly unrelated uses. It is a kind of grab-bag for retrieving all kinds of numerical information, internal to yabasic. The meaning of the numbers returned be the peek-function depends on the string or number passed as an argument.
peek always returns a number, however the closely related peek$-function exists, which may be used to retrieve string information from among the internals of yabasic. Finally note, that some of the values which are retrieved with peek may even be changed, using the poke-function.
There are two variants of the peek-function: One expects an integer, positive number and is described within the first entry of the list below. The other variant expects one of a well defined set of strings as described in the second and all the following entries of the list below.
peek(a)
Read a single byte (a number between 0 and 255) from the file a (which must be open of course). You may use the chr$-function to convert this byte to a string of one character.
As a special case, if the argument is zero: read a single byte from stdin.
peek("argument")
Return the number of arguments, that have been passed to yabasic at invocation time. E.g. if yabasic has been called like this: yabasic foo.yab bar baz, then peek("argument") will return 2. This is because foo.yab is treated as the name of the program to run, whereas bar and baz are considered arguments to the program, which are passed on the command line. Note, that for windows-users, who tend to click on the icon (as opposed to starting yabasic on the command line), this peekwill mostly return 0.
The function peek("argument") can be written as peek("arguments") too.
You will want to check out the corresponding function peek$("argument") to actually retrieve the arguments. Note, that each call to peek$("argument") reduces the number returned by peek("argument").
peek("error")
Return a number specifying the nature of the last error in an open- or seek-statement. Normally an error within an open-statement immediately terminates your program with an appropriate error-message, so there is no chance and no need to learn more about the nature of the error. However, if you use open as a condition (e.g. if (open(#1,"foo")) …) the outcome (success or failure) of the open-operation will determine, if the condition evaluates to true or false. If now such an operation fails, your program will not be terminated and you might want to learn the reason for failure. This reason will be returned by peek("error") (as a number) or by peek$("error") (as a string)
The table below shows the various error codes; the value returned by peek$("error") explains the nature of the error. Note, that the codes 10,11 and 12 refer to the seek-command.
Table 7.1. Error codes
peek("error")
|
peek$("error")
|
Explanation |
|---|---|---|
| 2 |
Stream already in use
|
Do not try to open one and the same filenumber twice; rather close it first. |
| 3 |
'x' is not a valid filemode
|
The optional filemode argument, which may be passed to the open-function, has an invalid value |
| 4 |
could not open 'foo'
|
The open-call did not work, no further explanation is available. |
| 5 |
reached maximum number of open files
|
You have opened more files than your operating system permits. |
| 6 |
cannot open printer: already printing graphics
|
The commands open printer and open #1,printer both open a printer (refer to their description for the difference). However, only one can be active at a time; if you try to do both at the same time, you will receive this error. |
| 7 |
could not open line printer
|
Well, it simply did not work. |
| 9 |
invalid stream number
|
An attempt to use an invalid (e.g. negative) stream number; example: open(-1,"foo") |
| 10 |
could not position stream x to byte y
|
seek did not work. |
| 11 |
stream x not open
|
You have tried to seek within a stream, that has not been opened yet. |
| 12 |
seek mode 'x' is none of begin,end,here
|
The argument, which has been passed to seek is invalid. |
peek("fontheight")
Return the height of the font used within the graphic window. If none is open, this peek will return the height of the last font used or 10, if no window has been opened yet.
peek("screenheight")
Return the height in characters of the window, wherein yabasic runs. If you have not called clear screen yet, this peekwill return 0, regardless of the size of your terminal.
peek("screenwidth")
Return the width in characters of the window, wherein yabasic runs. If you have not called clear screen yet, this peekwill return 0, regardless of the size of your terminal.
peek("secondsrunning")
Return the number of seconds that have passed since the start of yabasic.
peek("millisrunning")
Return the number of milliseconds, that have passed since the start of yabasic.
peek("version")
Return the version number of yabasic, e.g. 2.77. See also the related peek$("version"), which returns nearly the same information (plus the patchlevel) as a string, e.g. "2.77.1".
peek("winheight")
Return the height of the graphic-window in pixels. If none is open, this peek will return the height of the last window opened or 100, if none has been opened yet.
peek("winwidth")
Return the width of the graphic-window in pixels. If none is open, this peek will return the width of the last window opened or 100, if none has been opened yet.
peek("isbound")
Return true, if the executing yabasic-program is part of a standalone program; see the section about creating a standalone-program for details.
peek("version")
Return the version number of yabasic (e.g. 2.72).
peek("last_foreign_function_call_okay")
Check for error: If passing "no_error" to foreign_function_call, any error (e.g. failure to load the specified library), will not terminate your yabasic-program but rather store a descriptive error message away for later retrieval. Later on you may then check peek("last_foreign_function_call_okay") to find out, if something went wrong and retrieve a description with peek$("last_foreign_function_call_error_text").
This peek can be abbreviated as peek("last_frnfn_call_okay")
open "foo" for reading as #1
open "bar" for writing as #2
while not eof(#1)
poke #2,chr$(peek(#1));
wend
This program will copy the file foo byte by byte to bar.
Note, that each peek does something entirely different, and only one has been demonstrated above. Therefore you need to make up examples yourself for all the other peeks.
peek$ — retrieve various internal string-information
print peek$("foo")
The peek$-function has many different and unrelated uses. It is a kind of grab-bag for retrieving all kinds of string information, internal to yabasic; the exact nature of the strings returned be the peek$-function depends on the string passed as an argument.
peek$ always returns a string, however the closely related peek-function exists, which may be used to retrieve numerical information from among the internals of yabasic. Finally note, that some of the values which are retrieved with peek$ may even be changed, using the poke-function.
The following list shows all possible arguments to peek$:
peek$("infolevel")
Returns either "debug", "note", "warning", "error" or "fatal", depending on the current infolevel. This value can be specified with an option on the command line or changed during the execution of the program with the corresponding poke; however, normally only the author of yabasic (me !) would want to change this from its default value "warning".
peek$("textalign")
Returns one of nine possible strings, specifying the default alignment of text within the graphics-window. The alignment-string returned by this peek describes, how the text-command aligns its string-argument with respect to the coordinates supplied. However, this value does not apply, if the text-command explicitly specifies an alignment. Each of these strings is two characters long. The first character specifies the horizontal alignment and can be either l, r or c, which stand for left, right or center. The second character specifies the vertical alignment and can be one of t, b or c, which stand for top, bottom or center respectively.
You may change this value with the corresponding command poke "textalign",…; the initial value is lb, which means the top of the left and the top edge if the text will be aligned with the coordinates, that are specified within the text-command.
peek$("windoworigin")
This peek returns a two character string, which specifies the position of the origin of the coordinate system of the window; this string might be changed with the corresponding command poke "windoworigin",x,y or specified as the argument of the origin command; see there for a detailed description of the string, which might be returned by this peek.
peek$("program_name")
Returns the name of the yabasic-program that is currently executing; typically this is the name, that you have specified on the commandline, but without any path-components. So this peek$ might return foo.yab. As a special case when yabasic has been invoked without the name of a program to be executed this peek will return the literal strings standard input or, when also the option -e has been specified, command line. See also peek$("program_file_name") and peek$("interpreter_path") for related information.
peek$("program_file_name")
Returns the full file-name of the yabasic-program that is currently executing; typically this is the name, that you have specified on the commandline, including any path-components. For the special case, that you have bound your yabasic-program with the interpreter to a single standalone executable, this peek$ will return its name. See also peek$("program_name") and peek$("interpreter_path") for related information.
peek$("interpreter_path")
Return the full file-name of the yabasic-interpreter that is currently executing your program; typically this will end on yabasic or yabasic.exe depending on your platform and the path will be where you installed yabasic. For bound programs (see creating a standalone-program) however, this may be different and will include whatever you specified during the bind-command.
See also peek$("program_name") and peek$("program_file_name") for related information. Employing these, it would be possible for a yabasic-program to start itself: system(peek$("interpreter_path") + " " + peek$("program_file_name")). Of course, in this simple form this would be a bad idea, because this would start concurrent instances of yabasic without end.
peek$("error")
Return a string describing the nature of the last error in an open- or seek-statement. See the corresponding peek("error") for a detailed description.
peek$("library")
Return the name of the library, this statement is contained in. See the import-command for a detailed description or for more about libraries.
peek$("version")
Version of yabasic as a string; e.g. 2.77.1. See also the related peek("version"), which returns nearly the same information (minus the patchlevel) as a number, e.g. 2.77.
peek$("os")
This peek returns the name of the operating system, where your program executes. This can be either windows or unix.
peek$("font")
Return the name of the font, which is used for text within the graphic window; this value can be specified as the third argument to the open window-command.
peek$("env","NAME")
Return the environment variable specified by NAME (which may be any string expression). Which kind of environment variables are available on your system depends, as well as their meaning, on your system; however typing env on the command line will produce a list (for Windows and Unix alike). Note, that peek$("env",...) can be written as peek$("environment",...) too.
peek$("argument")
Return one of the arguments, that have been passed to yabasic at invocation time (the next call will return the the second argument, and so on). E.g. if yabasic has been called like this: yabasic foo.yab bar baz, then the first call to peek$("argument") will return bar. This is because foo.yab is treated as the name of the program to run, whereas bar and baz are considered arguments to this program, which are passed on the command line. The second call to peek$("argument") will return baz. Note, that for windows-users, who tend to click on the icon (as opposed to starting yabasic on the command line), this peekwill mostly return the empty string.
Note, that peek$("argument") can be written as peek$("arguments").
Finally you will want to check out the corresponding function peek("argument").
peek$("last_foreign_function_call_error_text")
Retrieve error text: If passing "no_error" to foreign_function_call, any error (e.g. failure to load the specified library), will not terminate your yabasic-program but rather store a descriptive error message away for later retrieval. Later on you may then check peek("last_foreign_function_call_okay") to find out, if something went wrong and retrieve a description with peek$("last_foreign_function_call_error_text").
This peek can be abbreviated as peek$("last_frnfn_call_error_text")
pi — a constant with the value 3.14159
print pi
pi is 3.14159265359 (well at least for yabasic); do not try to assign to pi (e.g. pi=22/7) this would not only be mathematically dubious, but would also result in a syntax error.
poke — change selected internals of yabasic
poke "foo","bar" poke "foo",baz poke #a,"bar" poke #a,baz
The poke-command may be used to change details of yabasic's behaviour. Like the related function peek, poke does many different things, depending on the arguments supplied.
Here are the different things you can do with poke:
poke 5,a
Write the given byte (a in the example above) to the specified stream (5#a in the example).
See also the related function function peek(1).
poke "dump","filename.dump"
Dump the internal form of your basic-program to the named file; this is only useful for debugging the internals of yabasic itself.
The second argument ("filename.dump"
in the example) should be the name of a file, that
gets overwritten with the dump, please be careful.
poke "fontheight",12
This poke changes the default fontheight. This can only have an effect, if the fonts given in the commands text or open window do not specify a fontheight on their own.
poke "font","fontname"
This poke specifies the default font. This can only have an effect, if you do not supply a fontname with the commands text or open window.
poke "infolevel","debug"
Change the amount of internal information, that yabasic outputs during execution.
The second argument can be either "debug", "note", "warning", "error" or "fatal". However, normally you will not want to change this from its default value "warning".
See also the related peek$("infolevel").
poke "random_seed",42
Set the seed for the random number generator; if you do this, the ran-function will return the same sequence of numbers every time the program is started.
poke "stdout","some text"
Send the given text to standard output. Normally one would use print for this purpose; however, sending e.g. control characters to your terminal is easier with this poke.
poke "textalign","cc"
This poke changes the default alignment of text with respect to the coordinates supplied within the text-command. However, this value does not apply, if the text-command explicitly specifies an alignment. The second argument ("cc" in the example) must always be two characters long; the first character can be one of l (left), r (right) or c (center); the second character can be either t (top), b (bottom) or c (center); see the corresponding peek$("textalign") for a detailed description of this argument.
poke "windoworigin","lt"
This poke moves the origin of the coordinate system of the window to the specified position. The second argument ("lt" in the example) must always be two characters long; the first character can be one of l (left), r (right) or c (center); the second character can be either t (top), b (bottom) or c (center). Together those two characters specify the new position of the coordinate-origin. See the corresponding peek$("windoworigin") for a more in depth description of this argument.
print "Hello, now you will see, how much work"
print "a simple for-loop involves ..."
input "Please press return " a$
poke "infolevel","debug"
for a=1 to 10:next a
This example only demonstrates one of the many pokes, which are described above: The program switches the infolevel to debug, which makes yabasic produce a lot of debug-messages during the subsequent for-loop.
print — Write to terminal or file
print "foo",a$,b
print "foo",a$,b;
print #a "foo",a$
print #a "foo",a$;
print foo using "##.###"
print reverse "foo"
print at(10,10) a$,b
print @(10,10) a$,b
print color("red","blue") a$,b
print color("magenta") a$,b
print color("green","yellow") at(5,5) a$,b
The print-statement outputs strings or characters, either to your terminal (also known as console) or to an open file.
To understand all those uses of the print-statement, let's go through the various lines in the synopsis above:
print "foo",a$,b
Print the string foo as well as the contents of the variables a$ and b onto the screen, silently adding a newline.
print "foo",a$,b;
(Note the trailing semicolon !) This statement does the same as the one above; only the implicit newline is skipped, which means that the next print-statement will append seamlessly.
print #a "foo",a$
This is the way to write to files. The file with the number a must be open already, an implicit newline is added. Note the file-number #a, which starts with a hash ('#') amd is separated from the rest of the statement by a space only. The file-number (contained in the variable a) must have been returned by a previous open-statement (e.g. a=open("bar")).
print #a "foo",a$;
The same as above, but without the implicit newline.
print foo using "##.###"
Print the number foo with as many digits before and after the decimal dot as given by the number of '#'-signs. See the entries for using and str$ for a detailed description of this format.
print reverse "foo"
As all the print-variants to follow, this form of the print-statement can only be issued after clear screen has been called. The strings and numbers after the reverse-clause are simply printed inverse (compared to the normal print-statement).
print at(10,10) a$,b
Print at the specified (x,y)-position. This is only allowed after clear screen has been called. You may want to query peek$("screenwidth") or peek$("screenheight") to learn the actual size of your screen. You may add a semicolon to suppress the implicit newline.
print @(10,10) a$,b
This is exactly the same as above, however, at may be written as @.
print color("red","blue") at(5,5) a$,b
Print with the specified fore- ("red") and background ("blue") color (or colour). The possible values are "black", "white", "red", "blue", "green", "yellow", "cyan" or "magenta". Again, you need to call clear screen first and add a semicolon if you want to suppress the implicit newline.
print color("magenta") a$,b
You may specify the foreground color only.
print color("green","yellow") a$,b
A color and a position (in this sequence, not the other way around) may be specified at once.
clear screen
columns=peek("screenwidth")
lines=peek("screenheight")
dim col$(7)
for a=0 to 7:read col$(a):next a
data "black","white","red","blue","green","yellow","cyan","magenta"
for a=0 to 2*pi step 0.1
print colour(col$(mod(i,8))) at(columns*(0.8*sin(a)+0.9)/2,lines*(0.8*cos(a)+0.9)/2) "*"
i=i+1
next a
This example draws a colored ellipse within the text window.
print color — print with color
print color(fore$) text$ print color(fore$,back$) text$
Not a separate command, but part of the print-command; may be included just after print and can only be issued after clear screen has been executed.
color() takes one or two string-arguments, specifying the color of the text and (optionally) the background.
The one or two strings passed to color() can be one of these: "black", "white", "red", "blue", "green", "yellow", "cyan" and "magenta" (which can be abbreviated as "bla", "whi", "red", "blu", "gre", "yel", "cya" and "mag" respectively).
color() can only be used, if clear scren has been issued at least once.
Note, that color() can be written as colour() too.
print colour — see print color
print colour(fore$) text$ print colour(fore$,back$) text$
putbit — draw a rectangle of pixels encoded within a string into the graphics window
open window 200,200 … a$=getbit(20,20,50,50) … putbit a$,30,30 putbit a$ to 30,30 putbit a$,30,30,"or"
The putbit-command is the counterpart of the getbit$-function. putbit requires a string as returned by the getbit-function. Such a string contains a rectangle from the graphic window; the putbit-function puts such a rectangular region back into the graphic-window.
Note, that the putbit-command currently accepts a fourth argument. However only the string value "or" is supported here. The effect is, that only those pixel, which are set in the string will be set in the graphic window. Those pixels, which are not set in the string, will not change in the window (as opposed to being cleared).
repeat
read d$
c$ = c$ + d$
until( d$ = "")
open window 200,200
do
x=ran(220)-10
y=ran(220)-10
putbit c$,x,y,"transparent"
loop
data "rgb 21,21:00000000000000000000000000000000000000000000000000000000000000"
data "32c800000000000000000000000000000000000000000000000000000000000000000000"
data "00000000000000000000000000000032c80032c80032c80032c80032c80032c80032c800"
data "32c80032c800000000000000000000000000000000000000000000000000000000000000"
data "32c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c800"
data "00000000000000000000000000000000000000000000000032c80032c80032c80032c800"
data "32c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c800000000"
data "00000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c8c8"
data "ff000032c80032c80032c80032c80032c80032c80032c800000000000000000000000000"
data "00000032c80032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8"
data "ff000032c80032c80032c80032c80032c80000000000000000000032c80032c80032c800"
data "32c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c800"
data "32c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8"
data "ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c800"
data "32c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8"
data "ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c800000000000000"
data "32c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8"
data "ff00c8ff00c8ff000032c80032c80032c80032c80000000032c80032c80032c80032c8c8"
data "ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff0000"
data "32c80032c80032c80032c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8"
data "ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c800"
data "32c80000000000000032c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8"
data "ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c800000000000000"
data "32c80032c80032c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8"
data "ff00c8ff00c8ff000032c80032c80032c80032c80000000000000032c80032c80032c800"
data "32c80032c8c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c800"
data "32c80032c80032c80032c80000000000000000000032c80032c80032c80032c80032c8c8"
data "ff00c8ff00c8ff00c8ff00c8ff00c8ff00c8ff000032c80032c80032c80032c80032c800"
data "00000000000000000000000032c80032c80032c80032c80032c80032c80032c80032c800"
data "32c80032c80032c80032c80032c80032c80032c80032c800000000000000000000000000"
data "00000000000032c80032c80032c80032c80032c80032c80032c80032c80032c80032c800"
data "32c80032c80032c80032c80032c800000000000000000000000000000000000000000000"
data "32c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c80032c800"
data "00000000000000000000000000000000000000000000000000000000000000000032c800"
data "32c80032c80032c80032c80032c80032c80032c80032c800000000000000000000000000"
data "000000000000000000000000000000000000000000000000000000000000000000000000"
data "0000000000000000000000000000000000000000000000000000000000000000"
data ""
This program uses a precanned string (containing the image of a blue circle with a yellow centre) and draws it repeatedly into the graphic-window. The mode "transparent" ensures, that no pixels will be cleared.
There are two possible values for the third argument of putbit. Both modes differ in the way, they replace (or not) any pixels from the window with pixels from the bitmap having the background colour.
transparent or t
With this mode the pixels from the window will be kept, if the bitmap contains pixels with background colour at this position; i.e. the bitmap is transparent
solid or s
With this mode the pixels from the window will be overpainted with the pixels from the bitmap in any case; i.e. the bitmap is solid
If you omit this argument, the default transparent applies.
putscreen — draw a rectangle of characters into the text terminal
clear screen … a$=getscreen$(5,5,10,10) … putscreen a$,7,7
The putscreen-command is the counterpart of the getscreen$-function. putscreen requires a string as returned by the getscreen-function. Such a string contains a rectangular detail from the terminal; the putscreen-function puts such a region back into the terminal-window.
Note, that clear screen must have been called before.
data-statements
dim
repeat-loop
data-pointer
ran() — return a random number
print ran() x=ran(y)
The ran-function returns a random number. If no argument is given, the number returned is in the range from 0 to 1; where only 0 is a possible value; 1 will never be returned. If an argument is supplied, the number returned will be in the range from 0 up to this argument, whereas this argument itself is not a possible return value. Regardless of the range, ran is guaranteed to have exactly 2**30 different return values.
If you call ran multiple times during your program, the sequence of random numbers will be different each time you invoke your program; however, if, e.g. for testing you prefer to always have the same sequence of random numbers you may issue poke "random_seed",123.
clear screen
c=peek("screenwidth")-1
l=peek("screenheight")
dim col$(8)
for a=0 to 7:read col$(a):next a
data "black","white","red","blue","green","yellow","cyan","magenta"
do
x=ran(c)
y=l-ran(l*exp(-32*((x/c-1/2)**2)))
i=i+1
print color(col$(mod(i,8))) at(x,y) "*";
loop
This example will print a colored bell-curve.
read — read data from data-statements
read a$,a … data "Hello !",7
The read-statement retrieves literal data, which is stored within data-statements elsewhere in your program.
read num
dim col$(num)
for a=1 to num:read col$(a):next a
clear screen
print "These are the colours known to yabasic:\n"
for a=1 to num
print colour(col$(a)) col$(a)
next a
data 8,"black","white","red","blue"
data "green","yellow","cyan","magenta"
This program prints the names of the colors known to yabasic in those very colors.
rectangle — draw a rectangle
open window 100,100 rectangle 10,10 to 90,90 rectangle 20,20,80,80 rect 20,20,80,80 box 30,30,70,70 clear rectangle 30,30,70,70 fill rectangle 40,40,60,60 clear fill rectangle 60,60,40,40
The rectangle-command (also known as box or rect, for short) draws a rectangle; it accepts four parameters: The x- and y-coordinates of two facing corners of the rectangle. With the optional clauses clear and fill (which may appear together and in any sequence) the rectangle can be cleared and filled respectively.
open window 200,200
c=1
do
for phi=0 to pi step 0.1
if (c) then
rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
else
clear rectangle 100+100*sin(phi),100+100*cos(phi) to 100-100*sin(phi),100-100*cos(phi)
endif
sleep 0.1
next phi
c=not c
loop
This example draws a nice animated pattern; watch it for a couple of hours, to see how it develops.
redim — create an array prior to its first use. A synonym for dim
See the dim-command.
The redim-command does exactly the same as the dim-command; it is just a synonym. redim has been around in older versions of basic (not even yabasic) for many years; therefore it is supported in yabasic for compatibility reasons.
Please refer to the entry for the dim-command for further information.
rem — start a comment
rem Hey, this is a comment # the hash-sign too (at beginning of line) // even the double slash ' and the single quote (at beginning of line) print "Not a comment" # This is an error !! print "Not a comment":// But this is again a valid comment print "Not a comment" // even this. print "Not a comment" rem and this !
rem introduces a comment (like # or //), that extends up to the end of the line.
Those comments do not even need a colon
(':') in front of them; they (rem, #, ' (single quite) and //) all behave alike except for # and ', which may only appear at the very beginning of a line; therefore the fourth example in the synopsis above (print "Not a comment" # This is an error !!) is indeed an error.
Note, that rem is an abbreviation for remark. remark however is not a valid command in yabasic.
Finally note, that a comment introduced with '#' may have a special meaning under unix; see the entry for # for details.
repeat — start a repeat-loop
repeat … until …
The repeat-loop executes all the statements up to the final until-keyword over and over. The loop is executed as long as the condition, which is specified with the until-clause, becomes true. By construction, the statements within the loop are executed at least once.
restore — reposition the data-pointer
read a,b,c,d,e,f restore read g,h,i restore foo data 1,2,3 label foo data 4,5,6
The restore-command may be used to reset the reading of data-statements, so that the next read-statement will read data from the first data-statement.
You may specify a label with the restore-command; in that case, the next read-statement will read data starting at the given label. If the label is omitted, reading data will begin with the first data-statement within your program.
input "Which language (german/english) ? " l$
if (instr("german",l$)>0) then
restore german
else
restore english
endif
for a=1 to 3
read x,x$
print x,"=",x$
next a
label english
data 1,"one",2,"two",3,"three"
label german
data 1,"eins",2,"zwei",3,"drei"
This program asks to select one of those languages known to me (i.e. english or german) and then prints the numbers 1,2 and 3 and their textual equivalents in the chosen language.
return — return from a subroutine or a gosub
gosub foo … label foo … return sub bar(baz) … return quertz end sub
The return-statement serves two different (albeit somewhat related) purposes. The probably more important use of return is to return control from within a subroutine to the place in your program, where the subroutine has been called. If the subroutine is declared to return a value, the return-statement might be accompanied by a string or number, which constitutes the return value of the subroutine.
However, even if the subroutine should return a value, the return-statement need not carry a value; in that case the subroutine will return 0 or the empty string (depending on the type of the subroutine). Moreover, feel free to place multiple return-statements within your subroutine; it's a nice way of controlling the flow of execution.
The second (but historically first) use of return is to return to the position, where a prior gosub has left off. In that case return may not carry a value.
do
read a$
if (a$="") then
print
end
endif
print mark$(a$)," ";
loop
data "The","quick","brown","fox","jumped"
data "over","the","lazy","dog",""
sub mark$(a$)
if (instr(lower$(a$),"q")) return upper$(a$)
return a$
end sub
This example features a subroutine mark$, that returns its argument in upper case, if it contains the letter "q", or unchanged otherwise. In the test-text the word quick will end up being marked as QUICK.
The example above demonstrates return within subroutines; please see gosub for an example of how to use return in this context.
reverse — print reverse (background and foreground colors exchanged)
clear screen … print reverse "foo"
reverse may be used to print text in reverse. reverse is not a separate command, but part of the print-command; it may be included just after the print and can only be issued once that clear screen has been issued.
right$() — return (or change) the right end of a string
print right$(a$,2) right$(b$,2)="baz"
The right$-function requires two arguments (a string and a number) and returns the part from the right end of the string, whose length is specified by its second argument. So, right$ simply returns the requested number of chars from the right end of the given string.
Note, that the right$-function can be assigned to, i.e. it may appear on the left hand side of an assignment. In this way it is possible to change a part of the variable used within the right$-function. Note, that that way the length of the string cannot be changed, i.e. characters might be overwritten, but not added. For an example see below.
print "Please enter a length either in inch or centimeter"
print "please add 'in' or 'cm' to mark the unit."
input "Length: " a$
if (right$(a$,2)="in") then
length=val(a$)*2.56
elsif (right$(a$,2)="cm") then
length=val(a$)
else
error "Invalid input: "+a$
endif
This program allows the user to enter a length qualified with a unit (either inch or centimeter).
This second example demonstrates the capability to assign to the right$-function.
a$="Heiho World !" print a$ right$(a$,7)="dwarfs." print a$
rinstr() — find the rightmost occurrence of one string within the other
pos=rinstr("Thequickbrownfox","equi")
pos=rinstr(a$,b$,x)
The rinstr-function accepts two string-arguments and tries to find the second within the first. However, unlike the instr, the rinstr-function finds the rightmost (or last) occurrence of the string; whereas the instr-function finds the leftmost (or first) occurrence. In any case however, the position is counted from the left.
If you supply a third, numeric argument to the rinstr-function, it will be used as a starting point for the search. Therefore rinstr("abcdeabcdeabcde","e",8) will return 5, because the search for an "e" starts at position 8 and finds the first one at position 5.
round() — round its argument to the nearest integer
print round(x)
The found-function returns the nearest integer (e.g. 3.0 for an argument of 2.6). An argument with a fractional part of 0.5 (e.g. 2.5) represents an edge case, as such an argument has the same distance to two numbers, 3.0 and 2.0 in the example; this ambiguity is resolved by rounding away from zero and returning 3.0. By the same rule round(-2.5) returns -3.0; so you see, that round(x) always equals round(-x).
rtrim$() — trim spaces at the right end of a string
a$=rtrim$(b$)
The rtrim$-function removes all whitespace from the right end of a string and returns the result.
open 1,"foo"
dim lines$(100)
l=1
while not eof(1)
input #1 a$
a$=rtrim$(a$)
if (right$(line$,1)="\\") then
line$=line$+" "+a$
else
lines$(l)=line$
l=l+1
line$=a$
endif
end while
print "Read ",l," lines"
This example reads the file foo allowing for continuation lines, which are marked by a \, which appears as the last character on a line. For convenience whitespace at the right end of a line is trimmed with rtrim.
clear screen clears the text window
screen — as clear screen clears the text window
clear screen
The keyword screen appears only within the sequence clear screen; please see there for a description.
seek() — change the position within an open file
open 1,"foo" seek #1,q seek #1,x,"begin" seek #1,y,"end" seek #1,z,"here"
The seek-command changes the position, where the next input (or peek) statement will read from an open file. Usually files are read from the beginning to the end sequentially; however sometimes you may want to depart from this simple scheme. This can be done with the seek-command, allowing you to change the position, where the next piece of data will be read from the file.
seek accepts two or three arguments: The first one is the number of an already open file. The second one is the position where the next read from the file will start. The third argument is optional and specifies the the point from where the position (the second argument) will count. It can be one of:
begin
Count from the beginning of the file.
end
Count from the end of the file.
here
Count from the current position within the file.
open #1,"count.dat","w"
for a=1 to 10
print #1,"00000000";
if (a<10) print #1,";";
next a
dim count(10)
do
x=int(ran(10))
i=i+1
if (mod(i,1000)=0) print ".";
count(x)=count(x)+1
curr$=right$("00000000"+str$(count(x)),8)
seek #1,9*x,"begin"
print #1,curr$;
loop
This example increments randomly one of ten counters (in the array count()); however, the result is always kept and updated within the file count.dat, so even in case of an unexpected interrupt, the result will not be lost.
sig() — return the sign of its argument
a=sig(b)
clear screen
dim c$(3):c$(1)="red":c$(2)="white":c$(3)="green"
do
num=ran(100)-50
print color(c$(2+sig(num))) num
loop
This program prints an infinite sequence of random number; positive numbers are printed in green, negative numbers are printed red (an exact zero would be printed white). (With a little extra work, this program could be easily extended into a brokerage system)
sin() — return the sine of its single argument
y=sin(angle)
open window 200,200
new curve
for phi=0 to 2*pi step 0.1
line to 100+90*sin(phi),100+90*cos(phi)
next phi
close curve
This program draws a circle (ignoring the existence of the circle-command).
shl() — shift its argument bitwise to the left
print shl(0b11001,8)
The shl-function (shl stands for shift left) treats its first argument as a binary number and shifts it to the left as specified by its second argument, filling up the gaps with zeroes. So bin$(shl(0b11011,4)) returns 110110000 (the example uses bin$ and a number with base 2).
Please note: as the argument of the function is converted to a 32-bit integer, all results are also confined to this range.
shr() — shift its argument bitwise to the right
print shr(0b110010000,4)
The shr-function (shr stands for shift right) treats its first argument as a binary number and shifts it to the right as specified by its second argument; the rightmost binary digits are discarded during this operation. So bin$(shr(0b1101100,2)) returns 11011 (the example uses bin$ and a number with base 2).
Please note: as the argument of the function is converted to a 32-bit integer, all results are also confined to this range.
sleep — pause, sleep, wait for the specified number of seconds
sleep 4
The sleep-command has many different names: You may write pause, sleep or wait interchangeably; whatever you write, yabasic will always do exactly the same.
Therefore you should refer to the entry for the pause-function for further information.
split() — split a string into many strings
dim w$(10) … num=split(a$,w$()) num=split(a$,w$(),s$)
The split-function requires a string (containing the text to be split), a reference to a string-array (which will receive the resulting strings, i.e. the tokens) and an optional string (with a set of characters, at which to split, i.e. the delimiters).
The split-function regards its first argument (a string) as a list of tokens separated by delimiters and it will store the list of tokens within the array-reference you have supplied. Note, that the array, which is passed as a reference (w$() in the synopsis), will be resized accordingly, so that you don't have to figure out the number of tokens in advance. The element at position zero (i.e. w$(0)) will not be used.
normally (i.e. if you omit the third, which is the delimiter-argument) the function will regard space or tab as delimiters for tokens; however by supplying a third argument, you may split at any single of the characters within this string. E.g. if you supply ":;" as the third argument, then colon (:) or semicolon (;) will delimit tokens.
Note, that a sequence of separator-characters will produce a sequence of empty tokens; that way, the number of tokens returned will always be one plus the number of separator characters contained within the string. Refer to the closely related token-function, if you do not like this behaviour. In some way, the split-function focuses on the separators (other than the token-function, which focuses on the tokens), hence its name.
The second argument is a reference on a string-array, where the tokens will be stored; this array will be expanded (or shrunk) to have room for all tokens, if necessary.
The first argument finally contains the text, that will be split into tokens. The split-function returns the number of tokens that have been found.
Please see the examples below for some hints on the exact behaviour of the split-function and how it differs from the token-function:
print "This program will help you to understand, how the"
print "split()-function exactly works and how it behaves"
print "in certain special cases."
print
print "Please enter a line containing tokens separated"
print "by either '=' or '-'"
dim t$(10)
do
print
input "Please enter a line: " l$
num=split(l$,t$(),"=-")
print num," Tokens: ";
for a=1 to num
if (t$(a)="") then
print "(EMPTY)";
else
print t$(a);
endif
if (a<num) print ",";
next a
print
loop
This program prints the following output:
Please enter a line: a 1 Tokens: a Please enter a line: 0 Tokens: Please enter a line: ab 1 Tokens: ab Please enter a line: a=b 2 Tokens: a,b Please enter a line: a- 2 Tokens: a,(EMPTY) Please enter a line: a-= 3 Tokens: a,(EMPTY),(EMPTY) Please enter a line: =a- 3 Tokens: (EMPTY),a,(EMPTY) Please enter a line: a=-b 3 Tokens: a,(EMPTY),b Please enter a line: a--b- 4 Tokens: a,(EMPTY),b,(EMPTY) Please enter a line: -a==b-c== 7 Tokens: (EMPTY),a,(EMPTY),b,c,(EMPTY),(EMPTY)
sqr() — compute the square of its argument
a=sqr(b)
The sqr-function computes the square of its numerical argument (i.e. it multiplies its argument with itself).
Please note, that other dialects of basic use sqr as the square root, rather than the square; this needs to be checked especially when porting programs from other Versions of basic.
sqrt() — compute the square root of its argument
to be written
static — preserves the value of a variable between calls to a subroutine
sub foo() static a … end sub
The static keyword can be used within subroutines to mark variables as static. This has two effects: First, the variable is local to the subroutine, i.e. its value is not know outside the subroutine (this is the effect of the local keyword). Second, the static-keyword arranges things, so that the variable keeps its value between invocations of the subroutine (this is different from the local-keyword).
foo()
foo()
foo()
sub foo()
static a
local b
a=a+1
b=b+1
print a,b
end sub
This program shows the difference between static and local variables within a subroutine; it produces this output:
1 1 2 1 3 1
The output shows, that the static variable a keeps its value between subroutine calls, whereas b is initialized with the value 0 at every call to the subroutine foo.
step — specifies the increment step in a for-loop
for a=1 to 10 step 3 … next a
Specify, by which amount the loop-variable of a for-loop will be incremented at each step.
The step (as well as the lower and upper bound) are computed anew in each step; this is not common, but possible, as the example below demonstrates.
str$() — convert a number into a string
a$=str$(a) b$=str$(x,"##.###") b$=str$(x,"###,###.##","_.") c$=str$(x,"%g")
The str$-function accepts a numeric argument and returns it as a string.
Note: As a special and trivial case str$ also accepts a single string-argument, which it just returns unchanged; this can be useful e.g. when used with eval$, see the example there for an application.
For the common case of converting a number to a string, the process can be controlled with an optional third argument (the format argument). See the following table of examples to learn about valid values of this argument. Note, that those examples fall in one of two categories: C-style and basic-style; the first 4 examples in the table below are C-style, the rest of the examples are basic-style. For more information on the C-style formats, you may refer to your favorite documentation on the C programming language. The basic-style formats are much simpler, they just depict the desired output, marking digits with '#'; groups of (usually three) digits may be separated with colons (','), the decimal dot must be marked by a literal dot ('.'). Moreover these characters (colons and dot) may be replaced by other characters to satisfy the needs of non-english (e.g. german) languages; see the examples below.
Note, that for clarity, each space in the result has been replaced by the letter 'x', because it would be hard to figure out, how many spaces are produced exactly otherwise.
Table 7.2. Examples for the format argument
Example string
|
Result for converting 1000*
|
Description
|
|---|---|---|
%g
|
3141.59
|
Internally yabasic uses double precision, so its numbers can be formatted with the %g format specifier. |
%2.5f
|
3141.59265
|
The '2' determines the minimum length of the output; but if needed (as in the example) the output can be longer. The '5' is the number of digits after the decimal point. |
%12.5f
|
xx3141.59265
|
Two spaces (which appear as 'x') are added to pad the output to the requested length of 12 characters. |
%012.5g
|
0000003141.6
|
The 'g' requests, that the precision ('5') specifies the overall number of digits (before and after the decimal point). |
%-12.5f
|
3141.59265xx
|
The '-' requests the output to be left-centered (therefore the filling space appears at the right). |
#####.##
|
x3141.59
|
Each '#' specifies a digit (either before or after the dot), the '.' specifies the position of the dot. As 1000*pi does not have enough digits, the 5 requested digits before the dot are filled up with a space (which shows up as an 'x'). |
##,###.##
|
x3,141.59
|
Nearly the same as above, but the colon from the format shows up within the result. |
##,###.## and an additional argument of ".," |
x3.141,59
|
Similar to the example above, but colon and dot are replaced with dot and colon respectively. |
##,###.## and an additional argument of "_," |
x3_141,59
|
Similar to the example above, but colon and dot are replaced with underscore and colon respectively. |
#####
|
x3142
|
The format string does not contain a dot, and therefore the result does not have any fractional digits. |
##.###
|
##.###
|
As 1000*pi has 4 digits in front of the decimal dot and the format only specifies 2, yabasic does not know what to do; therefore it chooses just to reproduce the format string. |
sub — declare a user defined subroutine
foo(2,"hello") … sub foo(bar,baz$) … return qux … end sub
The sub-keyword starts the definition of a user defined subroutine. With user defined subroutines you are able to somewhat extend yabasic with your own commands or functions. A subroutine accepts arguments (numbers or strings) and returns a number or a string (however, you are not required to assign the value returned to a variable).
The name of the subroutine follows after the keyword sub. If the name (in the synopsis: foo) ends on a '$', the subroutine should return a string (with the return-statement), otherwise a number.
After the name of the subroutine
yabasic requires a pair of braces; within those
braces you may specify a list of parameters, for which values can (but need
not) be included when calling the subroutine. If you omit one of those
parameters when calling such a subroutine, it assumes the value zero (for
numeric parameters) or the empty string (for string-parameters). However from
the special variable numparams you may find out, how many arguments have really been passed when calling the subroutine.
Parameters of a subroutine are always local variables (see the keyword local for more explanation).
From within the subroutine you may return any time with the keyword return; along with the return-keyword you may specify the return value. Note that more than one return is allowed within a single subroutine.
Finally, the keyword end sub ends the subroutine definition. Note, that the definition of a subroutine need not appear within the program before the first call to this sub.
As braces have two uses in yabasic (i.e. for supplying arguments to a subroutine as well as to list the indices of an array). yabasic can not tell apart an array from a subroutine with the same name. Therefore you cannot define a subroutine with the same name as an array !
switch — select one of many alternatives depending on a value
switch a case 1 case 2 … end switch … switch a$ case "a" case "b" end switch
The switch-statement selects one of many codepaths depending on a numerical or string expression. I.e. it takes an expression (either numeric or string) and compares it with a series of values, each wrapped within a case-clause. If the expression equals the value given in a case-clause, the subsequent statements are executed.
The default-clause allows one to specify commands, which should be executed, if none of case-clauses matches.
Note, that many case-clauses might be clustered (e.g. case "a":case "b":case "c"). Or put another way: You need a break-statement at the end of a case-branch, if you do not want to run into the next case.
input "Please enter a single digit: " n
switch n
case 0:print "zero":break
case 1:print "one":break
case 2:print "two":break
case 3:print "three":break
case 4:print "four":break
case 5:case 6: case 7:case 8:case 9
print "Much !":break
default:print "Hey ! That was more than a single digit !"
end switch
This example translates a single digit into a string; note, how the cases 5 to 7 are clustered.
system() — hand the name of an external command over to your operating system and return its exitcode
ret=system("foo")
system("bar")
The system-command accepts a single string argument, which specifies a command to be executed. The function will return the exitcode of the command; its output (if any) will be lost.
system$() — hand the name of an external command over to your operating system and return its output
print system$("dir")
The system$-command accepts a single string argument, specifying a command, that can be found and executed by your operating system. It returns the output of this command as one big string.
if-statement
tan() — return the tangent of its argument
foo=tan(bar)
The tan-function computes the tangent of its arguments (which should be specified in radians).
tell — get the current position within an open file
open #1,"foo" … position=tell(#1)
The tell-function requires the number of an open file as an argument. It returns the position (counted in bytes, starting from the beginning of the file) where the next read will start.
text — write text into your graphic-window
text x,y,"foo" text x,y,"foo","lb" text x,y,"foo","cc","font" text x,y,"foo","font","rt"
The text-commands displays a text-string (the third argument) at the given position (the first two arguments) within an already opened window. The font to be used can be optionally specified as either the fourth or fifth argument ("font" in the example above). A font specified this way will also be used for any subsequent text-commands, as long as they do not specify a font themselves.
The fourth or fifth optional argument ("lb" in the example above) can be used to specify the alignment of the text with respect to the specified position. This argument is always two characters long: The first character specifies the horizontal alignment and can be either l, r or c, which stand for left, right or center. The second character specifies the vertical alignment and can be one of t, b or c, which stand for top, bottom or center respectively. If you omit this alignment argument, the default "lb" applies; however this default may be changed with poke "textalign","xx"
open window 500,200
clear screen
data "lt","lc","lb","ct","cc","cb","rt","rc","rb"
for a=1 to 9
read align$
print "Alignment: ",align$
line 50*a-15,100,50*a+15,100
line 50*a,85,50*a,115
text 50*a,100,"Test",align$
inkey$
next a
This program draws nine crosses and writes the same text at each; however it goes through all possible nine alignment strings, showing their effect.
then — tell the long from the short form of the if-statement
if (a<b) then … endif
The keyword then is part of the if-statement; please see there for further explanations. However, not every if-statement requires the keyword then: If the keyword then is present, the if-clause may extend over more than one line, and the keyword endif is required to end it. If the keyword then is not present, the if-statement extends up to the end of the line, and any endif would be an error.
time$ — return a string containing the current time
print time$ print time$()
The time$ function returns the current time in four fields separated by hyphens '-'. The fields are:
The current hour in the range from 0 to 23, padded with zeroes (e.g. 00 or 04) to a length of two characters.
The number of minutes, padded with zeroes.
The number of seconds, padded with zeroes.
The number of seconds, that have elapsed since the program has been started. This value increases as long as your program runs and is therefore unbound and not padded with zeroes.
At the time of writing this documentation, time$ returns 22-58-53-0. Note, that the first three of the four fields returned by time$ have a fixed width; therefore it is easy to extract some fields with the usual string-functions mid$ (and others).
print "Hello it is ",time$
print "An empty for-loop with ten million iterations takes ";
for a=1 to 10000000:next a
print "Now it is ",time$
print peek("secondsrunning")," seconds have passed."
This program benchmarks the for-loop; however, it does not use the fourth field of the string returned by time$, because that string wraps around every 60 seconds; rather the peek "secondsrunning" is queried.
to — this keyword appears as part of other statements
for a=1 to 100 step 2 … next a line x,y to a,b
The to-keyword serves two purposes (which are not related at all):
within for-statements, to specify the upper bound of the loop.
Within any graphical command (e.g. line), that requires two points (i.e. four numbers) as arguments, a comma ',' might be replaced with the keyword to. I.e. instead of 100,100,200,200 you may write 100,100 to 200,200 in such commands.
token() — split a string into multiple strings
dim w$(10) … num=token(a$,w$()) num=token(a$,w$(),s$)
The token-function accepts a string (containing the text to be split), a reference to a string-array (which will receive the resulting strings, i.e. the tokens) and an optional string (with a set of characters, at which to split, i.e. the delimiters).
The token-function regards its first argument as a list of tokens separated by delimiters and it will store the list of tokens within the array-reference that has been supplied. Note, that the array, which is passed as a reference (w$() in the synopsis), will be resized accordingly, so that you don't have to figure out the number of tokens in advance. The element at position zero (i.e. w$(0)) will not be used.
Normally (i.e. if you omit the third, the delimiter-argument) the function will regard space or tab as delimiters for tokens; however by supplying a third argument, you may split at any single of the characters within this string. E.g. if you supply ":;" as the third argument, then colon (:) or semicolon (;) will delimit tokens.
Note, that token will never produce empty tokens, even if two or more separators follow in sequence. Refer to the closely related split-function, if you do not like this behaviour. In some way, the token-function focuses on the tokens and not on the separators (other than the split-function, which focuses on the separators).
The second argument is a reference on a string-array, where the tokens will be stored; this array will be expanded (or shrunk) as necessary to have room for all tokens.
The first argument finally contains the text, that will be split into tokens. The token-function returns the number of tokens, that have been found.
Please see the examples below for some hints on the exact behaviour of the token-function and how it differs from the split-function:
print "This program will help you to understand, how the"
print "token()-function exactly works and how it behaves"
print "in certain special cases."
print
print "Please enter a line containing tokens separated"
print "by either '=' or '-'"
dim t$(10)
do
print
input "Please enter a line: " l$
num=token(l$,t$(),"=-")
print num," Tokens: ";
for a=1 to num
if (t$(a)="") then
print "(EMPTY)";
else
print t$(a);
endif
if (a<num) print ",";
next a
print
loop
This program prints the following output:
Please enter a line: a 1 Tokens: a Please enter a line: 0 Tokens: Please enter a line: ab 1 Tokens: ab Please enter a line: a=b 2 Tokens: a,b Please enter a line: a- 1 Tokens: a Please enter a line: a-= 1 Tokens: a Please enter a line: =a- 1 Tokens: a Please enter a line: a=-b 2 Tokens: a,b Please enter a line: a--b- 2 Tokens: a,b Please enter a line: -a==b-c== 3 Tokens: a,b,c
triangle — draw a triangle
open window 100,100 triangle 100,100,50,50,100,50 fill triangle 50,100,100,50,200,200 clear fill triangle 20,20,10,10,200,200
The triangle-command draws a triangle; it requires 6 parameters: The x- and y-coordinates of the three points making up the triangle. With the optional keywords clear and fill (which may appear both and in any sequence) the triangle can be cleared and filled respectively.
open window 200,200
do
phi=phi+0.2
i=i+2
color mod(i,255),mod(85+2*i,255),mod(170+3*i,255)
dx=100*sin(phi):dy=20*cos(phi)
fill triangle 100+20*sin(phi),100+20*cos(phi),100-20*sin(phi),100-20*cos(phi),100-80*cos(phi),100+80*sin(phi)
sleep 0.1
loop
This example draws a colored triangles until you get exhausted.
trim$() — remove leading and trailing spaces from its argument
a$=trim$(b$)
The trim$-function removes all whitespace from the left and from the right end of a string and returns the result. Calling trim$ is equivalent to calling rtrim$(ltrim$()).
true — a constant with the value of 1
okay=true
The constant true can be assigned to variables which will later appear in conditions (e.g. an if-statement.
true may also be written as TRUE or even TrUe.
until — end a repeat-loop
repeat … until …
The until-keyword ends a loop, which has been introduced by the repeat-keyword. until requires an expression (see here for details) as an argument; the loop will continue until this condition evaluates to true.
upper$() — convert a string to upper case
u$=upper$(a$)
line input "Please enter a sentence without the letter 'e': " l$
p=instr(upper$(l$),"E")
if (p) then
l$=lower$(l$)
mid$(l$,p,1)="E"
print "Hey, you are wrong, see here!"
print l$
else
print "Thanks."
endif
This program asks for a sentence and marks the first (if any) occurrence of the letter 'e' by converting it to upper case (in contrast to the rest of the sentence, which is converted to lower case).
using — Specify the format for printing a number
print a using "##.###"
print a using("##.###",",.")
The using-keyword may appear as part of the print-statement and specifies the format (e.g. the number of digits before and after the decimal dot), which should be used to print the number.
The possible values for the format argument ("##.###" in the synopsis above) are described within the entry for the str$-function; especially the second line in the synopsis (print a using("##.###",",.")) will become clear after referring to str$. In fact the using clause is closely related to the str$-function; the former can always be rewritten using the latter; i.e. print foo using bar$ is always equivalent to print str$(foo,bar$). Therefore you should check out str$ to learn more.
val() — converts a string to a number
x=val(x$)
The val-function checks, if the start of
its string argument forms a floating point number and then returns this
number. The string therefore has to start with digits (only whitespace in front is allowed), otherwise the val-function returns zero.
input "Please enter a length, either in inches (in) or centimeters (cm) " l$
if (right$(l$,2)="in") then
l=val(l$)*2.51
else
l=val(l$)
print "You have entered ",l,"cm."
This example queries for a length and checks, if it has been specified in inches or centimeters. The length is then converted to centimeters.
while-loop
wait — pause, sleep, wait for the specified number of seconds
wait 4
The wait-command has many different names: You may write pause, sleep or wait interchangeably; whatever you write, yabasic will always do exactly the same.
Therefore you should refer to the entry for the pause-function for further information.
wend — end a while-loop
while a<b … wend
The wend-keyword marks the end of a while-loop. Please see the while-keyword for more details.
wend can be written as end while or even end-while.
while — start a while-loop
while … … wend
The while-keyword starts a while-loop, i.e. a loop that is executed as long as the condition (which is specified after the keyword while) evaluates to true.
Note, that the body of such a while-loop will not be executed at all, if the condition following the while-keyword is not true initially.
If you want to leave the loop prematurely, you may use the break-statement.
origin — move the origin of a window
open window 200,200 origin "cc"
The origin-command applies to graphic windows and moves the origin of the coordinate system to one of nine point within the window. The normal position of the origin is in the upper left corner of the window; however in some cases this is inconvenient and moving the origin may save you from subtracting a constant offset from all of your coordinates.
However, you may not move the origin to an arbitrary position; in horizontal position there are only three positions: left, center and right, which are decoded by the letters l, c and r. In vertical position the allowed positions are top, center and bottom; encoded by the letters t, c and b. Taking the letters together, you arrive at a string, which might be passed as an argument to the command; e.g. "cc" or "rt".
xor() — compute the exclusive or
x=xor(a,b)
The xor-function computes the bitwise exclusive or of its two numeric arguments. To understand the result, both arguments should be viewed as binary numbers (i.e. a sequence of digits 0 and 1); a bit of the result will then be 1, if exactly one argument has a 1 and the other has a 0 at this position in their binary representation.
Note, that both arguments are silently converted to integer values and that negative numbers have their own binary representation and may lead to unexpected results when passed to and.
print xor(7,4)
This will print 3. This result is obvious, if you note, that the binary representation of 7 and 4 are 111 and 100 respectively; this will yield 011 in binary representation or 2 as decimal.
The eor-function is the same as the xor-function; both are synonymous; however they have each their own description, so you may check out the entry of eor for a slightly different view.
# — either a comment or a marker for a file-number
# This is a comment, but the line below not ! open #1,"foo"
The hash ('#') has two totally unrelated uses:
A hash might appear in commands related with file-io. yabasic uses simple numbers to refer to open files (within input, print, peek or eof). In those commands the hash may precede the number, which species the file. Please see those commands for further information and examples; the rest of this entry is about the second use (as a comment).
As the very first character within a line, a hash introduces comments (similar to rem).
'#' as a comment is common in most scripting languages and has a special use under Unix: If the very first line of any Unix-program begins with the character sequence '#!' ("she-bang", no spaces allowed), the rest of the line is taken as the program that should be used to execute the script. I.e. if your yabasic-program starts with '#!/usr/local/bin/yabasic', the program /usr/local/bin/yabasic will be invoked to execute the rest of the program. As a remark for windows-users: This mechanism ensures, that yabasic will be invoked to execute your program; the ending of the file (e.g. .yab) will be ignored by Unix.
// — starts a comment
// This is a comment !
The double-slash ('//') is (besides REM and '#') the third way to start a comment. '//' is the latest and greatest in the field of commenting and allows yabasic to catch up with such cool languages like C++ and Java.
// Another comment.
print "Hello world !" // Another comment
Unlike the example given for '#' this example is syntactically correct and will not produce an error.
: — separate commands from each other
print "Hello ":print "World"
The colon (':') separates multiple commands on a single line.
The colon and the newline-character have mostly the same effect, only that the latter, well, starts a new line too. The only other difference is their effect within the (so-called) short if, which is an if-statement without the keyword then. Please see the entry for if for more details.
; — suppress the implicit newline after a print-statement
print "foo",bar;
The semicolon (';') may only appear at the last position within a print-statement. It suppresses the implicit newline, which yabasic normally adds after each print-statement.
Put another way: Normally the output of each print-statement appears on a line by itself. If you rather want the output of many print-statements to appear on a single line, you should end the print-statement with a semicolon.
** or ^ — raise its first argument to the power of its second
print 2**b print 3^4
** (or ^, which is an
exact synonym), is the arithmetic operator of exponentiation; it requires one
number to its left and a second one to its right; ** then
raises the first argument to the power of the second and returns the
result. The result will only be computed if it yields a real number (as opposed to a complex number); this means, that the power can not be computed, if the first argument is negative and the second one is fractional. On the other hand, the second argument can be fractional, if the first one ist positive; this means, that ** may be used to compute arbitrary roots: e.g. x**0.5 computes the square root of x.
The program below is a very simple program:
repeat input "Please enter the first number, to add " a input "Please enter the second number, to add " b print a+b until a=0 and b=0
This program requests two numbers, which it than adds. The process is repeated until you enter zero (or nothing) twice.
yabasic allows to retrieve and put back rectangular regions of the screen with simple commands:
open window 200,200
rem prepare picture of a star
dim p(3,2)
for off=0 to 90 step 30
for a=0 to 2
phi = (off + 120*a)*2*pi/360
p(a,0) = 50 + 20*cos(phi)
p(a,1) = 50 + 20*sin(phi)
next a
fill triangle p(0,0),p(0,1),p(1,0),p(1,1),p(2,0),p(2,1)
next off
star$ = getbit$(30,30,80,80)
clear window
for a=0 to 200 step 10
line a,0 to a,200:line 0,a to 200,a: rem draw some pattern on the screen
next a
for a=10 to 150 step 5
saved$=getbit$(a,80,a+40,120): rem save old content of window
putbit star$ to a,80,"t": rem put star at new location
pause 0.5
putbit saved$ to a,80: rem restore old window content
next a
This program moves moves the picture of a star across the graphics window. The first part of the program draws such a star and then retrieves the bitmap with getbit$(). Yabasic stores bitmaps within ordinary strings and so the star-bitmap can simply be stored within the variable star$.
Once the program has prepared the bitmap-string, it puts it back into the window with the putbit-command and various locations. Each time before the star-bitmap is put into the window, the prior content is saved within the variable saved$ and restored later.
This example program presents a menu (e.g. a predefined set of 3 choices) and lets the user choose one of them. The menu is similar (but simpler) to the one employed in the demo of yabasic
// Initialize menu
restore menudata
read menusize:dim menutext$(menusize)
for a=1 to menusize:read menutext$(a):next a
ysel=1
clear screen
blank$ = " "
hash$ = "########################################"
print colour("cyan","magenta") at(7,2) hash$
print colour("cyan","magenta") at(7,3) hash$
print colour("cyan","magenta") at(7,4) hash$
print colour("yellow","blue") at(8,3) " This is a simple menu to choose from "
for a=1 to menusize
if (a=menusize) then yoff=1:else yoff=0:fi
if (a=ysel) then
print colour("blue","green") at(5,7+yoff+a) menutext$(a);
else
print at(5,7+yoff+a) menutext$(a);
endif
next a
print at(3,15) "Select with cursor keys UP or DOWN (or letters u and d),"
print at(3,16) "Press RETURN or SPACE to choose, ESC to quit."
do
k$=inkey$
yalt=ysel
switch k$
case "up":case "u":
if (ysel=1) then ysel=menusize else ysel=ysel-1 fi
redraw()
break
case "down":case "d":
if (ysel=menusize) then ysel=1 else ysel=ysel+1 fi
redraw()
break
case " ":case "enter":case "right":
if (ysel=menusize) end_it()
print at(3,18) "You have chosen: " + menutext$(ysel) + blank$
sleep 1
print at(3,18) blank$ + blank$
break
case "esc":
end_it()
default:
print at(3,18) "Invalid key: " + k$ + blank$
sleep 1
print at(3,18) blank$ + blank$
end switch
loop
// redraw line
sub redraw()
local yoff
if (yalt=menusize) then yoff=1:else yoff=0:fi
print at(5,7+yalt+yoff) menutext$(yalt);
if (ysel=menusize) then yoff=1:else yoff=0:fi
print colour("blue","green") at(5,7+ysel+yoff) menutext$(ysel);
return
end sub
// terminate program
sub end_it()
print at(3,18) "Bye ..."
sleep 1
exit
end sub
// Data section ...
label menudata
// Data for main menu: Number and text of entries in main menu
data 4
data " First Item "
data " Item number two "
data " Last Item "
data " None of the above "
Some interesting aspects from top to bottom:
The text of the various menu-items is initialized at the top of the program; the needed text-strings are kept in data-lines at the end of the program.
User-input is aquired with the inkey$-function.
A switch-statement is employed to process the input; several keys (e.g. right and enter) are handled in the same case-clause.
Two subroutines redraw() and end_it() handle common work, that needs to be done at multiple places in the program.
yabasic may be copied under the terms of the MIT License, which is distributed with yabasic in the file LICENSE.
The MIT License grants extensive rights as long as you keep the copyright notice present in most files untouched. Here is a list of things that are possible under the terms of the MIT License:
Put yabasic on your own homepage or CD and even charge for the service of distributing yabasic.
Write your own yabasic-programs, pack your program and yabasic into a package and sell the whole thing.
Modify yabasic and add or remove features, sell the modified version without adding the sources.