String comparison: Difference between revisions

All character comparisons are literal: case counts. There is no facility for case insensitive comparison (though in principle a compiler could offer to do so via non-standard mnemonics) and there often are no library routines for case conversion. The usual procedure is to copy both items to scratch variables (with all the annoyance of "how big?"), convert both to upper case (or both to lower case) and then compare. Or, rather than copying the strings, one might code for a character-by-character comparison and handling case differences one character at a time. With single-character comparison one can use ICHAR(''c'') to obtain the numerical value of the character code, and this enables the use of the three-way test of the arithmetical-IF as in <code>IF (ICHAR(TEXT1(L:L)) - ICHAR(TEXT2(L:L))) ''negative'',''equal'',''positive''</code>, where ''negative'' would be the statement label jumped to should character L of TEXT2 be greater than character L of TEXT1. With equality, one would increment L and after checking that TEXT1 and TEXT2 had another character L available, test afresh. Further, to accommodate case insensitivity, one could prepare an array of 256 integers, say UC, where UC(''i'') = ''i'' except for the indices corresponding to the character code values of the lower case letters which instead have those of the upper case letters. Then the comparison might be <code>IF (UC(ICHAR(TEXT1(L:L))) - UC(ICHAR(TEXT2(L:L)))) ''negative'',''equal'',''positive''</code> whereby case insensitivity is achieved without the annoyance of multiple testing or case conversion but at the cost of array access. And by re-arranging values in array UC, a custom ordering of the character codes could be achieved at no extra cost.