there's an error in the last line of your code:

print "oero+oero: ", $oero-$oero, "\n";

although you're printing "oero+oero, you're calculating $oero-$oero, which is not the same, because if $oero was any number, subtracting itself would probably yield 0. instead, it should read

print "oero+oero: ", $oero+$oero, "\n";

which fortunately, evaluates as 0, and stands as a good example of 0 but true.

~Particle