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Date: Fri, 30 May 1997 08:00:17 -0400 (EDT)
From: Thomas David Rivers <ponds!rivers@dg-rtp.dg.com>
Message-Id: <199705301200.IAA11334@lakes.water.net>
To: ponds!FreeBSD.ORG!hackers, ponds!anchorage.net!un_x
Subject: Re: cc/gcc
Content-Type: text
Sender: owner-hackers@FreeBSD.ORG
X-Loop: FreeBSD.org
Precedence: bulk

> 
> 
> with cc/gcc, i get outputs of "1" and "0" respectively.  why?
> is this construct ABSOLUTELY incorrect, or is something else amuck?
> /*****************************************************************************/
> #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);
>      a='1'; b='1'; c = 0;
>      c = a == b == '1' ? '1' : '0'; printf(" %c\n", c);
> 
> exit( 0 );}
> /*****************************************************************************/
> 
> 

 I believe '?' has a higher precedence than '=='; so you are
really saying:

  is b equal to:
	if 1 then
		1
	else
	   0
   compare b and 1 - they are the same.
	-> yes
  is a equal b?
   compare a with the result of b's compare (1 == 1)?
	-> yes
  assign the 'yes' to c.
	c <= 1

Then, in the second case:

>      c = a == b == '1' ? '1' : '0'; printf(" %c\n", c);

  is b equal to:
	if 0x31 then
	  0x31
	else
	  0x30
   compare b and 0x31 - they are the same.


  is a iequal to 1 (the result of the b == ..)
	-> no ('a' is 0x31, the result of the boolean is 1)

  c is assigned the result of the comparison with a and 1
	c <= 0

  So, c gets the value 0 in the second case.


Does that help?

	- Dave Rivers -