IBM System/36 BASIC

These core BASIC statements, functions, and commands were used:

DATA

DIM

END

FOR...NEXT

GOSUB...RETURN

GOTO

IF...THEN

INPUT

LET

ON...GOTO

PRINT

PRINT USING

READ

REM

STOP

ASC()

RND()

SIN()

COS()

TAN()

TAB()

SQRT()

LOG()

LIST

More advanced IBM-supplied statements included:

ON ERROR Allows error trapping

OPTION Permits program-wide properties such as Base 1 or Base 0 array indexing, long or short precision, etc.

OPEN Allows a file or device (formatted workstation, printer) to be opened

CLOSE Closes a file or device

WRITE Outputs to a file or device

REWRITE Changes a record or display format

APPEND Adds to a file

DELETE Deletes a record from a file

IMAGE Defines the format of a record using COBOL-like syntax

FORM Defines the format of a record using RPG-like syntax

DEF FN..FNEND Defines a function

CHAIN Loads and passes control to another BASIC program

PRINT #255: Prints to the (default) printer file

PRINT NEWPAGE Clears the screen

PRINT #255: NEWPAGE Advances to the next page on the printer file

AIDX() Refers to the ascending index of an array, which is an array of relative sorted pointers to array elements

DIDX() Same as AIDX but uses a descending index

SRCH() Used to find a value in an array by retrieving the match pointer

SRCH$() Used to find a string value in a string array by retrieving the match pointer

RENUMBER A command used to renumber the lines within a program

LOAD A command used to load a program from a library on the fixed disk

SAVE A command used to save a program to a library on the fixed disk

OFF A command used to exit the interactive BASIC session

LISTP A command used to list the current program to the printer

{{code|ON ERROR}} is an error-trapping statement that allows BASIC to suspend an error that might otherwise stop a BASIC program from running and perform an error-handling routine instead. Variants include suffixing {{mono|OFLOW, ZDIV}}, and other error types to a statement and immediately trap these errors.

{{mono|OPTION}} allows the BASIC program to meet special criteria. Sometimes BASIC did not have very much user space (since all S/36 programs are limited to 64K) and the area called "code space" which contains the current user program must reside within the user space. Therefore, users could choose {{code|OPTION LPREC}} which causes BASIC to compute with double-precision (long) numerics, or {{code|OPTION SPREC}} which provides more space and single-precision (short) numerics. Some programmers prefer matrix mathematics where the lowest-numbered index is 0, others prefer 1. {{code|2=basic|OPTION BASE 0}} and {{code|2=basic|OPTION BASE 1}} accomplish this. There are other uses for {{mono|OPTION}}.

RPG II programs on the S/34 and S/36 could not call each other, but BASIC programs could, using the {{mono|CHAIN}} statement. {{mono|CHAIN}} passes control from the current BASIC module to the named module, bearing a list of arguments which can become variables in the new module when it is loaded.

{{code|2=basic|DEF FN}} allows the definition of a user function in BASIC which can be named and referred in the program. {{mono|FNEND}} is placed after the last statement in a function.

There are four ways to format BASIC input and output. First, unformatted; just {{mono|PRINT}} and {{mono|INPUT}} to your heart's content. Second, with {{code|2=basic|PRINT USING}}, which in S/36 BASIC can incorporate a constant, a string variable, a line number, or a label. Third, with {{code|2=basic|PRINT FIELDS}} and {{code|2=basic|INPUT FIELDS}}, which place 5250-type display fields on the CRT in immediate mode. Fourth, by using a workstation file (opened with {{code|2=basic|1=OPEN #x: "WS,NAME="}} and so forth) and performing various combinations of {{mono|WRITE}} and {{mono|READ}} to that workstation file, using SDA-generated screen formats similar to those in other S/36 applications. {{mono|WRITE}} and {{mono|READ}}, as well as {{code|2=basic|PRINT USING}} and {{code|2=basic|INPUT USING}}, can direct BASIC to a line number or a label that contains the keyword {{code|IMAGE:}}.

An IMAGE statement contains decimals, commas, dollar signs, dashes, and pound signs ("#") in representation of the substituted numeric or alphameric values.

{{sxhl|2=bbcbasic|1=

3540 IMAGE: ###-##-#### ############################# $#,###,###.##

}}

A FORM statement denotes the size of the variables to be read or written. To save a numeric value of .00 to 99,999.99, use this notation:

{{sxhl|2=basic|1=

2959 FORM N 7.2

}}

A label is a tag on a line as follows:

{{sxhl|2=bbcbasic|1=

260 BEGIN_CALCULATIONS::

270 FOR X = 1 TO 12

280 Y = Y + X*1.08

290 NEXT X

}}

If desired, the statement {{code|GOSUB BEGIN_CALCULATIONS}} can be used instead of {{code|GOSUB 260}}.

{{mono|OPEN, CLOSE, WRITE, REWRITE, DELETE,}} and {{mono|APPEND}} are already familiar to COBOL programmers and describe the actions taken to access S/36 disk files using BASIC. It isn't possible to access every single type of S/36 file because these include system files, libraries, and folders, but every user-created S/36 file with a fixed record length (only FORTRAN programs can use variable record lengths) will suffice. Disk files can be opened sequentially, by index, or relatively (by record number). If a file is delete-capable, records can be deleted using the {{mono|DELETE}} statement. To add a record, use {{mono|WRITE}} (with {{mono|APPEND}} specified in the {{mono|OPEN}} statement) and to update use {{mono|REWRITE}}.

In S/36 BASIC, to print to the printer, a device file must be used. A default printer file called #255 always exists when BASIC is started. It has a printer name of BASIC255 and opens the device that is the default printer for the terminal that begins a BASIC session. If desired, it is possible to create a different printer file numbered between 1 and 254. Use {{code|2=basic|1=OPEN #x: PRINTER,NAME=}} and so forth to do this, specifying columns or device ID or other parameters as needed. The {{mono|PAGEOFLOW}} keyword can be used to trap the page overflow condition for the printer.

Some versions of BASIC allow the programmer to sort an array. S/36 BASIC doesn't provide a function for this, but it does provide an interesting remedy. The programmer can define an array with the same number of elements as the target array and use AIDX or DIDX to create an ascending or descending index. Each element of the new array will contain a number representing the ordinal sorted position of the target array, so if AMERICA is the sixth element of array {{mono|A$}} but first in alphabetical order, then setting {{code|1=A() = DIDX(A$)}} would cause {{code|A(6)}} to contain the value 1.

Writing a BASIC program is much more fun than rewriting the same program each time you use it, therefore the authors of BASIC allow programmers to {{mono|SAVE}} their program code to a library member and to {{mono|REPLACE}} it when changes are made.

{{code|2=basic|SAVE PROG1,PGMRLIB}} causes the current module to be saved as a subroutine member (type R) named {{mono|PROG1}} in a user library named {{mono|PGMRLIB}}.

Note that System/36 files are not part of libraries. If a disk file is named {{mono|FNF001}}, then an {{mono|OPEN}} statement like this one can work:

{{sxhl|2=basic|1=

OPEN #3:"NAME=FNF001,SEQUENTIAL",INPUT

}}

It doesn't matter which library is used to access file FNF001.

{{mono|RENUMBER}} is the S/36 BASIC command used to renumber statements. All internal references to statement numbers are immediately recalculated.

System/36 BASIC has a very dangerous command called {{mono|FREE}}. Typing {{mono|FREE}} followed by a filename deletes that file without a trace. It will work for every user file, unless there is a conflict of security or an in-use condition that blocks it.

System/36 BASIC has another dangerous command called {{mono|LOCK}}. The {{mono|LOCK}} command will make the current program source code inaccessible and it is not reversible. Always save an unlocked copy before using LOCK.

System/34 BASIC and System/36 BASIC are very similar; however, machine code incompatibility makes it impossible to port a subroutine member BASIC program between these systems.

See also Square Root of 2 & PI π solution for solution published on mainframes during the 1980s & 1990s.

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Category:BASIC interpreters

System 36 BASIC