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COBOL General discussion FAQ
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Conditionals
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Does order matter in conditional expressions?
Posted: 7 Mar 02
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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:
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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