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From: cspw.quagga@p0.f4.n494.z5.fidonet.org (cspw quagga)
Newsgroups: comp.lang.modula2
Subject: Why are the loops so awkward?
Message-ID: <5377.26731960@puddle.fidonet.org>
Date: 9 Jun 90 21:04:56 GMT
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I've been coerced into writing a large application in Modula2 and my
confusions and biases are coming to the fore.
 
Can someone please comment on the following examples and tell
me whether I win the prize for the most abstruse interpretation
of the rules, or whether I have really understood the language
properly.  Problem: do something to every element in an array (say a string).
 
 PROCEDURE P(VAR S : ARRAY OF CHAR);
 VAR i,j   : INTEGER;
     k,n   : CARDINAL;
 BEGIN
    n := Length(S);
 
    FOR k := 0 TO n-1 DO
      process(S[k]);
    END;
    (* Wrong: For empty strings, n-1 is not a cardinal, or may be very big *)
 
    FOR i := 0 TO n-1 DO
       process(S[i]);
    END;
    (* Wrong: Can't mix INTEGER and CARDINAL in the same loop *)
 
    j := INTEGER(n);          (* Lets assume this is okay *)
    FOR i := 0 TO j-1 DO      (* The loop now goes correctly in all cases *)
       process(S[i]);
    END;
    (* Wrong: The index type of an open array is CARDINAL, so using
              an integer as a subscript is not strictly permitted. *)
 
    k := 0;
    WHILE (S[k] <> 0C) DO
       process(S[k]);
       INC(K);
    END;
      (* Wrong: Strings do not always store the trailing NUL byte. *)
 END P;
 
Am I in a grumpy mood without justifiable cause?
 
Pete



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