$a = 1;
$b = 0;

print "a=$a\tb=$b\n";
$a ^= 1;
$a ^= 1;
print "a=$a\tb=$b\n";

if($a eq 1)  { $a = 0 }  else { $a = 1 }
if($b eq 1)  { $b = 0 }  else { $b = 1 }

print "a=$a\tb=$b\n";