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Does order matter in conditional expressions?

Conditionals

Does order matter in conditional expressions?

by  k5tm  Posted    (Edited  )
Yes, it can matter.

The COBOL standard specifies an order in which the terms of the conditional expression are evaluated. The standard specifies left-to-right evaluation, and further specifies that evaluation terminates as soon as the value of the conditional expression can be determined.

The practical use of this is a situation wherein if the first term is TRUE the evaluation of the second term might result in a runtime error:
Code: 
PERFORM A-PARAGRAPH UNTIL
        A-SUBSCRIPT > SUBSCRIPT-LIMIT 
     OR A-TABLE (A-SUBSCRIPT) = SPACES.
In this example, the COBOL standard requires that A-SUBSCRIPT > SUBSCRIPT-LIMIT, the leftmost boolean term, be evaluated first and, if true, terminate evaluation (because the entire expression will be TRUE) before testing A-TABLE (A-SUBSCRIPT), thereby avoiding a potential runtime problem (referring beyond the last item in a table).
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