User:PauliKL/ANSI BASIC

ANSI BASIC is the standard published by the American National Standards Institute (ANSI) for the BASIC programming language. There are two standards: ANSI X3.60-1978 Minimal Basic and ANSI X3.113-1987 "Full Basic". These standards were subsequently adopted by International Organization for Standardization (ISO).

History

ANSI Full Basic

The Proposed Standard for Basic was published in the year 1983 .

Language constructs

Hello world

Unlike most other languages, typical BASIC implementations do not require any decorative constructs in the program. In ANSI BASIC, however, END instruction is mandatory.

BASIC does not need semicolons or similar to mark end of statement. Each statement ends at the end of line, unless line continuation character '\' is used. Unlike most real world Basic implementations, ANSI BASIC still requires line numbers.

Here is an example source code for a very simple Hello world program:

   10 PRINT "Hello, World"
   20 END

Control structures

ANSI BASIC is a structured programming language. Some of the basic control structures are described below.

Conditional statements:

   10 IF a > b THEN
   20     b = b*2
   30     sum = sum + a
   40 ELSE
   50     a = a+1
   60     sum = sum + b
   70 END IF
   
  100 SELECT CASE value
  110   CASE 1
  120     CALL do_something
  130   CASE 2,3,4
  140     CALL do_otherthing(value)
  150   CASE IS > 4
  150     counter = counter+1
  160     value = value/2
  170   CASE ELSE
  180     PRINT "Incorrect value"
  190 END SELECT 

Loops

The DO...LOOP structure by itself creates an endless loop. However, it may have an exit statement WHILE or UNTIL at the beginning and/or at the end. In addition, EXIT DO statement can be used to exit anywhere in the middle of the loop.

  200 DO
  210     PRINT question$
  220     INPUT answer$
  230     IF answer = "quit" THEN EXIT DO
  240     CALL check_answer(answer$)
  220 LOOP WHILE time_left
  

FOR...NEXT loop may have an optional step value. Exit from middle of the loop can be done with EXIT FOR.

  300 FOR row = 1 TO maxrows
  310     FOR column = 1 TO maxcols STEP 8
  320         PRINT TAB(column);"*";
  330     NEXT column
  340     PRINT
  350 NEXT row

Procedures and functions

ANSI BASIC has two types of procedures: SUBs and FUNCTIONs. The difference is that a FUNCTION returns a value, SUB does not. Both of them can be either internal or external. In internal procedure, all the variables are global within the program unit. In external procedure, all variables are local.

   500 SUB check_answer(answer$)
   510     IF answer$ = correct$ THEN
   520         PRINT "Correct!"
   530         score = score+1
   540         CALL NextQuestion
   550     ELSE
   560         PRINT "Wrong, try again."
   570     ENDIF
   580 END SUB