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From: mwm@eris.BERKELEY.EDU (Mike (My watch has windows) Meyer)
Newsgroups: comp.lang.c
Subject: Re: Possible C Anomaly
Message-ID: <5112@jade.BERKELEY.EDU>
Date: Wed, 16-Sep-87 04:03:08 EDT
Article-I.D.: jade.5112
Posted: Wed Sep 16 04:03:08 1987
Date-Received: Fri, 18-Sep-87 06:21:34 EDT
References: <9270@brl-adm.ARPA>
Sender: usenet@jade.BERKELEY.EDU
Reply-To: mwm@eris.BERKELEY.EDU (Mike (My watch has windows) Meyer)
Organization: Missionaria Phonibalonica
Lines: 47

In article <9270@brl-adm.ARPA> mrd@sun.mcs.clarkson.EDU (Michael R. DeCorte) writes:
<   /* Example #1 */            k = (k > 1) ? k-- : 1;
<
<   My intent was to decrement k with each pass until it reached 1 and then to
<   keep it at one.  There are a variety of ways to accomplish this but I just
<   happened to try this one first.

<Try 
<	k = (k > 1) ? --k : 1;

No! Consider that you're doing (one way) "k = --k". You still don't know
whether k will be decremented or assigned to first.

Even worse, this statement doesn't make a lot of sense. Try doing
another "equivalent" replacement, and get

	k = (k = k - 1)

Why would you want to write something like that?

<or
<	k = (k > 1) ? (k - 1) : 1;

Much better - it's right.

I've noticed that may C programmers overuse the "++" and "--"
operators. They're nice for changing the value of a variable by one
when you want to use the current/resulting value in another
expression. If you just want the decremented value, write "k - 1". You
can avoid stepping on your own toes that way. Likewise, if you really
don't want the value for later use, you might consider "k -= 1"
instead of "k--" or "--k".

Since this comes up at regular intervals, I think I'll repeat it here:

C *does not* guarantee the order of evaluation of an expressions,
except for the logical operators. Any expression that changes the
value of a variable more than once should be looked at with extreme
caution. If logicals don't force order of evaluation, then the
resulting code is *not* portable.

	<mike
--
Lather was thirty years old today,			Mike Meyer
They took away all of his toys.				mwm@berkeley.edu
His mother sent newspaper clippings to him,		ucbvax!mwm
About his old friends who'd stopped being boys.		mwm@ucbjade.BITNET