sub bin {
      my $num = shift;
      my $bin = "";

      for my $digit (128, 64, 32, 16, 8, 4, 2, 1) {
          if($num >= $digit) {
              $num -= $digit;
              $bin .= 1;
          } else {
              $bin .= 0;
          }
      }

      return $bin;
  }