Date: Fri, 30 May 1997 12:42:30 +0930 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: un_x@anchorage.net (Steve Howe) Cc: hackers@FreeBSD.ORG Subject: Re: cc/gcc Message-ID: <199705300312.MAA23760@genesis.atrad.adelaide.edu.au> In-Reply-To: <Pine.BSF.3.95q.970529180401.8774A-100000@aak.anchorage.net> from Steve Howe at "May 29, 97 06:10:28 pm"
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Steve Howe stands accused of saying:
>
> with cc/gcc, i get outputs of "1" and "0" respectively. why?
> is this construct ABSOLUTELY incorrect, or is something else amuck?
Well, apart from the fact that not using parentheses places you at the
mercy of precedence that you may not appreciate (see
/usr/share/misc/operator), let's have a look :
> /*****************************************************************************/
> #include "stdio.h"
> /*****************************************************************************/
> void main (unsigned char argc, unsigned char **argv) {
>
> unsigned char a, b, c;
>
> a = 1; b = 1; c = 0;
> c = a == b == 1 ? 1 : 0 ; printf(" %i\n", c);
No need to initialise c.
== groups left-to-right, has highest precedence.
a == b -> true
true == 1 -> true
true ? 1 : 0 -> 1
c = 1
> a='1'; b='1'; c = 0;
> c = a == b == '1' ? '1' : '0'; printf(" %c\n", c);
Likewise no need to initialise c.
a == b -> true
true == '1' -> false ***
false ? '1' : '0' -> '0'
c = '0'
It is generally unwise to try to cast a boolean (truth) value to a
scalar in any context.
--
]] Mike Smith, Software Engineer msmith@gsoft.com.au [[
]] Genesis Software genesis@gsoft.com.au [[
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