Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!lll-crg!lll-lcc!unisoft!dual!ucbvax!jade!eris!mwm
From: mwm@eris.BERKELEY.EDU (Mike (Don't have strength to leave) Meyer)
Newsgroups: comp.lang.c
Subject: Re: Not only that, but...
Message-ID: <1638@jade.BERKELEY.EDU>
Date: Tue, 11-Nov-86 16:04:56 EST
Article-I.D.: jade.1638
Posted: Tue Nov 11 16:04:56 1986
Date-Received: Wed, 12-Nov-86 20:31:55 EST
References: <166@houligan.UUCP>
Sender: usenet@jade.BERKELEY.EDU
Reply-To: mwm@eris.BERKELEY.EDU (Mike (Don't have strength to leave) Meyer)
Organization: Missionaria Phonibalonica
Lines: 26

In article <166@houligan.UUCP> dave@murphy.UUCP (H. Munster) writes:
>In article <630@dg_rtp.UUCP>, throopw@dg_rtp.UUCP (Wayne Throop) types:
>>Again folks, play it safe: *NEVER* have two side-effects on a single
>>object in a single expression.
>
>Not only that, but: don't even *USE* an assigned-to object anywhere else
>in the expression!

The first isn't quite sufficient, as Dave showed. But the second is an
over-reaction.  There are operators in C that are guaranteed to
preserve order, so you can make an assignment then use the variable
assigned to.

To wit, '||' and '&&' WILL be evaluated left-to-right (and short
circuit), so you can safely write:

	while ((c = getchar()) != TERMINATOR && c != EOF)
		;

Since leaving off the test for EOF is usually a bug, this is a
good thing. I know, this example can be rewritten as a do-while, and
you can move subsequent tests to the top of the loop with breaks. But
the first case isn't always true, and the second isn't as readable as
the above C idiom.

	<mike