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Groups > comp.lang.c > #148711
| From | David Brown <david.brown@hesbynett.no> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: for-loop mutates to an endless-loop |
| Date | 2020-01-03 15:34 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <qunjct$8vk$1@dont-email.me> (permalink) |
| References | <h78q9lF3mhkU1@mid.individual.net> <slrnr0ufpc.221.dan@djph.net> |
> Walter H. wrote:
>> [code]
>> #include <stdio.h>
>> int main( int argc, char* argv[ ] )
>> {
>> short int nIter;
>> long lSum = 0;
>> for ( nIter = -32768; nIter <= 32767; nIter++ )
>> lSum += nIter;
>> printf( "sum: %ld\n", lSum );
>> return 0;
>> }
>> [/code]
>
>> where is the mistake in C?
>
> Your stop condition -- "nIter <=32767" -- is incorrect. When
> the iterator is 32767, it is still true, and so you add "1". This
> causes it to roll over to -32768, and keep counting.
There is no guarantee that it will "roll over". /Maybe/ it will roll
over and keep counting. Maybe the compiler just notes that nIter can
never be greater than 32767, and realises that the loop will never end,
and then it can generate whatever code it likes - gcc with optimisation
generates a tight loop without any arithmetic at all, but it could have
generated an error message instead.
(With the sizes of "int" and "short" on these platforms, overflowing
"short" here will be implementation dependant behaviour which will
almost certainly be wrapping - but that is up to the compiler.
Overflowing "int" is undefined behaviour and is often /not/ wrapping.
Please do not give the impression that wrapping is normal or standard
behaviour - it will lead language newcomers to make mistakes.)
>
> Changing the line to:
>
> for (nIter = -32768; nIter < 32767; nIter++)
>
> should fix it for you.
It will cause the loop to terminate, but not with the expected answer.
>
> HTH :)
>
>
>
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for-loop mutates to an endless-loop "Walter H." <Walter.H-Nntp@mathemainzel.info> - 2020-01-03 13:27 +0100
Re: for-loop mutates to an endless-loop David Brown <david.brown@hesbynett.no> - 2020-01-03 14:01 +0100
Re: for-loop mutates to an endless-loop Dan Purgert <dan@djph.net> - 2020-01-03 13:18 +0000
Re: for-loop mutates to an endless-loop James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-03 08:28 -0500
Re: for-loop mutates to an endless-loop Dan Purgert <dan@djph.net> - 2020-01-03 13:33 +0000
Re: for-loop mutates to an endless-loop James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-03 21:10 -0500
Re: for-loop mutates to an endless-loop David Brown <david.brown@hesbynett.no> - 2020-01-03 15:34 +0100
Re: for-loop mutates to an endless-loop James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-03 08:26 -0500
Re: for-loop mutates to an endless-loop "Walter H." <Walter.H-Nntp@mathemainzel.info> - 2020-01-04 16:15 +0100
Re: for-loop mutates to an endless-loop David Brown <david.brown@hesbynett.no> - 2020-01-04 17:17 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-04 16:20 +0000
Re: for-loop mutates to an endless-loop "Walter H." <Walter.H-Nntp@mathemainzel.info> - 2020-01-04 18:43 +0100
Re: for-loop mutates to an endless-loop David Brown <david.brown@hesbynett.no> - 2020-01-04 19:28 +0100
Re: for-loop mutates to an endless-loop Bart <bc@freeuk.com> - 2020-01-04 18:59 +0000
Re: for-loop mutates to an endless-loop David Brown <david.brown@hesbynett.no> - 2020-01-05 14:24 +0100
Re: for-loop mutates to an endless-loop Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-04 13:47 -0800
Re: for-loop mutates to an endless-loop David Brown <david.brown@hesbynett.no> - 2020-01-05 14:26 +0100
Re: for-loop mutates to an endless-loop "Walter H." <Walter.H-Nntp@mathemainzel.info> - 2020-01-06 20:31 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-04 22:25 +0000
Re: for-loop mutates to an endless-loop Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2020-01-04 14:08 -0800
Re: for-loop mutates to an endless-loop James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-04 21:32 -0500
Re: for-loop mutates to an endless-loop scott@slp53.sl.home (Scott Lurndal) - 2020-01-05 21:48 +0000
Re: for-loop mutates to an endless-loop James Kuyper <jameskuyper@alumni.caltech.edu> - 2020-01-04 21:43 -0500
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-03 14:47 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-03 14:39 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-03 15:42 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-03 15:07 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-03 16:18 +0100
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-03 16:47 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-03 20:41 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 01:05 +0100
Re: for-loop mutates to an endless-loop gazelle@shell.xmission.com (Kenny McCormack) - 2020-01-03 18:30 +0000
Re: for-loop mutates to an endless-loop Robert Wessel <robertwessel2@yahoo.com> - 2020-01-04 00:23 -0600
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 08:10 +0100
Re: for-loop mutates to an endless-loop scott@slp53.sl.home (Scott Lurndal) - 2020-01-04 16:41 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 17:44 +0100
Re: for-loop mutates to an endless-loop Bart <bc@freeuk.com> - 2020-01-04 11:15 +0000
Re: for-loop mutates to an endless-loop Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-01-04 12:33 +0000
Re: for-loop mutates to an endless-loop "Walter H." <Walter.H-Nntp@mathemainzel.info> - 2020-01-04 15:59 +0100
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 16:01 +0100
Re: for-loop mutates to an endless-loop Jorgen Grahn <grahn+nntp@snipabacken.se> - 2020-01-04 16:04 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 17:06 +0100
Re: for-loop mutates to an endless-loop scott@slp53.sl.home (Scott Lurndal) - 2020-01-04 16:42 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 17:44 +0100
Re: for-loop mutates to an endless-loop Robert Wessel <robertwessel2@yahoo.com> - 2020-01-04 17:55 -0600
Re: for-loop mutates to an endless-loop "Walter H." <Walter.H-Nntp@mathemainzel.info> - 2020-01-06 20:43 +0100
Re: for-loop mutates to an endless-loop scott@slp53.sl.home (Scott Lurndal) - 2020-01-06 19:50 +0000
Re: for-loop mutates to an endless-loop Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2020-01-06 15:37 -0500
Re: for-loop mutates to an endless-loop scott@slp53.sl.home (Scott Lurndal) - 2020-01-06 21:59 +0000
Re: for-loop mutates to an endless-loop Robert Wessel <robertwessel2@yahoo.com> - 2020-01-06 17:33 -0600
Re: for-loop mutates to an endless-loop gazelle@shell.xmission.com (Kenny McCormack) - 2020-01-03 18:31 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 01:06 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-04 01:38 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 08:10 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-04 16:39 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 17:41 +0100
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-04 17:49 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-04 22:49 +0000
Re: for-loop mutates to an endless-loop Bonita Montero <Bonita.Montero@gmail.com> - 2020-01-05 03:44 +0100
Re: for-loop mutates to an endless-loop David Brown <david.brown@hesbynett.no> - 2020-01-04 13:09 +0100
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-03 14:28 +0000
Re: for-loop mutates to an endless-loop jak <nospam@please.ty> - 2020-01-05 00:40 +0100
Re: for-loop mutates to an endless-loop "Walter H." <Walter.H-Nntp@mathemainzel.info> - 2020-01-06 20:50 +0100
Re: for-loop mutates to an endless-loop Manfred <noname@add.invalid> - 2020-01-06 21:28 +0100
Re: for-loop mutates to an endless-loop Manfred <noname@add.invalid> - 2020-01-06 21:02 +0100
Re: for-loop mutates to an endless-loop Tim Rentsch <tr.17687@z991.linuxsc.com> - 2020-01-11 10:01 -0800
Re: for-loop mutates to an endless-loop Richard Damon <Richard@Damon-Family.org> - 2020-01-04 16:21 -0500
Re: for-loop mutates to an endless-loop Ben Bacarisse <ben.usenet@bsb.me.uk> - 2020-01-04 22:17 +0000
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