Topic       : The GFA-Basic Compendium
Author      : GFA Systemtechnik GmbH
Version     : GFABasic.HYP v2.98 (12/31/2023)
Subject     : Documentation/Programming
Nodes       : 899
Index Size  : 28056
HCP-Version : 3
Compiled on : Atari
@charset    : atarist
@lang       : 
@default    : Document not found
@help       : Help
@options    : +g -i -s +z
@width      : 75
@hostname   : STRNGSRV
@hostname   : CAB     
@hostname   : HIGHWIRE
@hostname   : THING   
View Ref-FileELSE IF condition

condition: bexp

The command ELSE IF enables nested IF's to be more clearly expressed in a
program. The following examples show a simple menu selection made on a single
key-press. If l, s, or e is pressed then, respectively, a load, save or, input
routine is called. In all other cases the message 'unknown command' is printed.
The normal nested version is as follows:

    DO
      t$=CHR$(INP(2))
      '
      IF t$="l"
        PRINT "Load text"
      ELSE
        IF t$="s"
          PRINT "Save text"
        ELSE
          IF t$="e"
            PRINT "Enter text"
          ELSE
            PRINT "unknown command"
          ENDIF
        ENDIF
      ENDIF
      '
    LOOP

The use of ELSE IF produces a shorter listing with smaller program indents:

    DO
      t$=CHR$(INP(2))
      '
      IF t$="l"
        PRINT "Load text"
      ELSE IF t$="s"
        PRINT "Save text"
      ELSE IF t$="e"
        PRINT "Enter text"
      ELSE
        PRINT "unknown command"
      ENDIF
      '
    LOOP

The program works in the following way:

If the condition after IF is fulfilled (t$="l"), then the instructions between
IF and the next ELSE IF are processed - PRINT "Load text" - and then the
program jumps to the command ENDIF. If the condition for the first IF is not
true then the other IF's are encountered.

In the second case, if the condition after the ELSE IF command is met, then all
instructions up to the next ELSE, ELSE IF or ENDIF (if no ELSE exists) are
processed and the program jumps to the instruction after ENDIF. If neither the
condition after the IF or the condition after ELSE IF is true, then the
commands between ELSE and ENDIF are implemented (if an ELSE exists).

Memo: This fails compiled:
      IF blah...
      ELSE IF FALSE  !the entire ELSE IF-ENDIF structure ends up missing!
      ELSE IF 0      !same issue!
      ENDIF
      Seems ok in the interpreter.