I suggest you test your code before posting:

use strict;
sub same_sign {
    my ($x,$y) = @_;
    if ( undef($x) or undef($y)) {
       return 0;           # "undef" is never same-sign
    }
    if (   ( ($x >= 0) and ($y >= 0) )
        or ( ($x <  0) and ($y <  0) ) )
    {
       return 1;
    }
    else 
    {
       return 0;
    }
  } 

$\ = "\n";
print same_sign(1,1);
print same_sign(0,0);
print same_sign(undef,undef);
print same_sign(-1,-1);
print same_sign(-2,-2);
print same_sign(2,-2);
__END__
1
1
1
1
1
1

[download]

Your subroutine seems to suggest that all values passed in always have the same value sign...

Update: Correction thanks to lodin

In reply to Re^2: Seeing if two numbers have the same sign by Corion
in thread Seeing if two numbers have the same sign by grinder

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