my $length = 0;
while (1) { 
   print "Enter the length: ";
   chomp ($length = <>);
   # checking for non-numeric characters
   unless ($length =~ /^[\d.]+$/){ 
      print "\nPlease enter a number\n";
      next;
   } 
   last if 0 <= $length and $length <= 99.99;
   print "It must be between 0 and 99.99\n";
}