$_ |  $r |  $.
Use of uninitialized value in printf at ./r2.pl line 12.
   a |   1 |    
   b |   2 |   1
   c |   3 |   2
   d |   4 |   3
   e | 5E0 |   4

  $_ |  $r |  $.
   a |   1 |   1
   b |   2 |   2
   c |   3 |   3
   d |   4 |   4
   e | 5E0 |   5