Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!aplcen!bink
From: bink@aplcen.apl.jhu.edu (Ubben Greg)
Newsgroups: comp.lang.c
Subject: Re: comma operator:  keep away?
Summary: Don't misuse the for(;;) expressions
Message-ID: <1104@aplcen.apl.jhu.edu>
Date: 24 Apr 89 01:08:48 GMT
References: <19913@iuvax.cs.indiana.edu> <10092@smoke.BRL.MIL> <19926@iuvax.cs.indiana.edu> <2179@pur-phy>
Reply-To: bink@aplcen.apl.jhu.edu (Greg Ubben)
Distribution: usa
Organization: The Johns Hopkins University, Baltimore MD
Lines: 26

In article <2179@pur-phy> (Sho Kuwamoto) writes:
>[...]
>As for another example where you could use the comma operator usefully,
>how about...
>
>	for(i=0, p=head; p->next != NULL; i++, p=p->next)
>or something.

Right idea, but bad example.  People too often cram expressions in the
for(;;) that are not related to the loop control, just to avoid a couple of
extra lines.  I admit that I do it myself.  In this case, the execution of
the loop is totally dependent on the contents of the linked list.  It would
be more clearly written as:
	i = 0;
	for (p=head; p->next!=NULL; p=p->next) {
		/*  I normally use "p" instead of "p->next!=NULL" */
		/*  We're skipping the last item here.            */
		i++;
	}
It's especially hard to resist this when the for expression would otherwise
be null.  I would be tempted to hide the i=0 in its declaration and the i++
in an expression, but this is arguably also bad.  Actually, I'm not all that
firm on this opinion.  Comments?

					-- Greg Ubben
					   bink@aplcen.apl.jhu.edu