> -----Original Message-----
> From: Charles Lu [SMTP:[EMAIL PROTECTED]]
> Sent: Wednesday, June 13, 2001 10:53 AM
> To: [EMAIL PROTECTED]
> Subject: Unexplainable behavior
>
> The following snippet of code doesn't behave the way I want it to. Yet i
> cannot see why?
>
>
> $hash{s} = "T";
>
>
> if(exists($hash{s}) and $hash{s} ne "T" or $hash{s} ne "F") {
> print "inside\n";
> }
> else{ print "outside\n"; }
>
>
This is a logic problem and can be explained by "De Morgan's Law".
Basically, if we analyze the if statement, it contains 3 parts.
exists($hash{s}) --> true
$hash{s} ne "T" --> false
$hash{s} ne "F" --> true
Hence, $hash{s} ne "T" or $hash{s} ne "F" --> true
And 'true' and 'true' --> true, so it goes 'inside'.
So you meant to only go inside if it does not equal
"T" or does not equal "F". This can be done by doing:
if(exists($hash{s}) and $hash{s} ne "T" and $hash{s} ne "F").
-Robin
