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Groups > comp.lang.c > #11332

behavior of || operator

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Hello,

#define ATTACH           1
#define DETACH           2

#define DIRECTION_INGRESS       1   /* Incoming */
#define DIRECTION_EGRESS        2   /* Outgoing */



if ((action != ATTACH) || (action != DETACH))

    puts("invalid action");

if ((dir != DIRECTION_INGRESS) || (dir != DIRECTION_EGRESS))
    puts("invalid direction");



I appears that condition within if() is verified for being TRUE or FALSE, 
and it is sufficient to have just one operand of || operator to return TRUE 
in order for the whole expression yield TRUE result.



For example, if action = 1, then (action != ATTACH) becomes FALSE, then 
(action != DETACH) is evaluated and it will return TRUE, thus making the 
statement within if() TRUE. And this is wrong behavior, given that I need to 
have actoni be either 1 or 2.



To make it right, || must be replaced with &&.



Is my reasoing above correct and valid?



Thanks.



Mark.

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behavior of || operator "Mark" <mark_cruzNOTFORSPAM@hotmail.com> - 2011-10-07 13:13 -0400
  Re: behavior of || operator James Kuyper <jameskuyper@verizon.net> - 2011-10-07 14:11 -0400
  Re: behavior of || operator John Gordon <gordon@panix.com> - 2011-10-07 18:47 +0000
  Re: behavior of || operator Willem <willem@toad.stack.nl> - 2011-10-07 19:50 +0000
  Re: behavior of || operator Gene <gene.ressler@gmail.com> - 2011-10-08 13:58 -0700

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