ZX BASIC:IF
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IF ... END IF
IF is a very powerful control flow sentence that allows you to make decisions under specified contitions.
Syntax
IF expression THEN sentences [ELSEIF expression THEN sentences] [ELSEIF expression THEN sentences] ... [ELSE sentences] END IF
Examples
IF a < 5 THEN PRINT "A is less than five" ELSE PRINT "A is greater than five" END IF
Sentences might be in multiple lines:
IF a < 5 THEN PRINT "A is less than five" a = a + 5 ELSE PRINT "A is greater than five" END IF
Since IF is a sentence, it can be nested; however, remember that every IF must be closed with END IF:
IF a < 5 THEN PRINT "A is less than five" IF a > 2 THEN PRINT "A is less than five but greater than 2" END IF ELSE IF a < 7 THEN PRINT "A is greater or equal to five, but lower than 7" ELSE PRINT "A is greater than five" END IF END IF
Using ELSEIF
In the example above, you see that nesting an IF inside another one could be somewhat verbose and error prone. It's better to use the ELSEIF construct. So the previous example could be rewritten as:
IF a < 5 THEN PRINT "A is less than five" IF a > 2 THEN PRINT "A is less than five but greater than 2" END IF ELSEIF a < 7 THEN PRINT "A is greater or equal to five, but lower than 7" ELSE PRINT "A is greater than five" END IF
Remarks
- This sentence is extended and not compatible with the Sinclair BASIC version: Every IF must be closed with END IF