Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!haven!adm!smoke!gwyn
From: gwyn@smoke.BRL.MIL (Doug Gwyn)
Newsgroups: comp.lang.c
Subject: Re: comma operator:  keep away?
Message-ID: <10098@smoke.BRL.MIL>
Date: 23 Apr 89 00:34:01 GMT
References: <19913@iuvax.cs.indiana.edu> <10092@smoke.BRL.MIL> <19926@iuvax.cs.indiana.edu>
Reply-To: gwyn@brl.arpa (Doug Gwyn)
Organization: Ballistic Research Lab (BRL), APG, MD.
Lines: 23

In article <19926@iuvax.cs.indiana.edu> bobmon@iuvax.cs.indiana.edu (RAMontante) writes:
>I find that neither one uses a comma in getc, getchar, putc, putchar, or
>anywhere else, except to separate parameters.

Ok, I picked a bad example.  However, many macros need to accomplish
more than one thing and cannot do so without the aid of some such
trickery as
	((expr1) & 0 | (expr2))
which is more simply expressed as
	(expr1, expr2)

>Nonetheless I think I get the idea, but that doesn't mean that the code
>wouldn't work without the comma (does it?) -- couldn't the same semantics
>be reproduced by a series of statements culminating in the final
>expression of the parentheses (presumably for assignment purposes)?

No!  A series of statements cannot be used as a subexpression.

Of course -- as I just demonstrated -- there are ways to avoid ever using
a comma operator, but then all you really need is a Turing machine, right?
So why does C provide more than the logical minimum?  It's because it was
designed to be USED for real programming, and matters of convenience are
quite relevant for that.