Path: utzoo!attcan!uunet!ncrlnk!ncrcae!hubcap!gatech!uflorida!haven!adm!xadmx!spector%BRILLIG.UMD.EDU@cunyvm.cuny.edu
From: spector%BRILLIG.UMD.EDU@cunyvm.cuny.edu (Lee Spector)
Newsgroups: comp.lang.pascal
Subject: Re: Control variables in FOR loops
Message-ID: <17855@adm.BRL.MIL>
Date: 16 Dec 88 21:31:21 GMT
Sender: news@adm.BRL.MIL
Lines: 56

In article <1440@csuna.UUCP> abcscnuk@csuna.UUCP (Naoto Kimura) writes:
>
>program nonsense(input,output);
>    var
>    i : integer;
>
>    procedure barf;
>    begin
>    for i := 1 to 10 do
>        write(i:3);
>    write('   i=',i)     (****)
>    end;
>
>    procedure ack;
>    begin
>    for i := 1 to 10 do begin
>        write('i=',i:2,' ');
>        barf;
>        writeln('i=',i:2)
>      end
>    end;
>
>begin
>    for i := 1 to 10 do
>    ack
>end.

(The question is: what SHOULD this do and what DOES it do in implementation
 X.)

I ran this on Berkeley pascal on a big Vax here at U. MD.  The compiler did not
complain.  I don't like what resulted from the last line in barf.
(the one I marked (****)  What it did was to always print 10.
This is not consistent with any rules for access to i that I can formulate.
I thought I understood how loop counters were supposed to work, but now
I'm quite confused and I'd appreciate any clarification anyone can offer.

(If all references to i are to the global - even asssuming that the
values that a loop counter takes on are precomputed and that the loop
variable is set to the proper value at the top of the loop - then
the last line in ack should also always print 10.
If entering a loop pushes a new activation record then the line in question
(****) refers to an uninitialized variable; this is not the case as
the result is the same even if you add a statement to initialize the global.)

(the output was the following repeated 10 times:)
i= 1   1  2  3  4  5  6  7  8  9 10   i=        10i= 1
i= 2   1  2  3  4  5  6  7  8  9 10   i=        10i= 2
i= 3   1  2  3  4  5  6  7  8  9 10   i=        10i= 3
i= 4   1  2  3  4  5  6  7  8  9 10   i=        10i= 4
i= 5   1  2  3  4  5  6  7  8  9 10   i=        10i= 5
i= 6   1  2  3  4  5  6  7  8  9 10   i=        10i= 6
i= 7   1  2  3  4  5  6  7  8  9 10   i=        10i= 7
i= 8   1  2  3  4  5  6  7  8  9 10   i=        10i= 8
i= 9   1  2  3  4  5  6  7  8  9 10   i=        10i= 9
i=10   1  2  3  4  5  6  7  8  9 10   i=        10i=10