{
  print "Number?\n";
  redo unless <STDIN> =~ /^\d+$/;
}

##</code><code>##

{
  print "Number?\n";
  redo unless <STDIN> =~ /^(\d+)$/ and $number=$1;
}

##</code><code>##

print "Number?\n" while <STDIN> !~ /^\d+$/;