#!/usr/bin/perl -w
use strict;
&a;
sub a{

  print "enter a number: ";
  chomp(my $a=<STDIN>);
 
  if ($a=~/[^\d]+/){ print "not a number!"; &a;
  } else { print "You typed: $a\n"; &a; }
}

##</code><code>##

#!/usr/bin/perl -w
use strict;
&a;
sub a{
ASK: print "enter a number: ";
     chomp(my $a=<STDIN>);

     if ($a=~/[^\d]/){ print "not a number!\n"; goto ASK;
     } else { print "you entered: $a\n"; goto ASK; }
}