use strict;
use warnings;

while (1)
  {
  print "\nEnter a number to add or multiply or nothing to exit: ";
  my $first = <STDIN>;
  chomp $first;

  last if 0 == length $first;

  print "Enter a second number: ";
  my $second = <STDIN>;
  chomp $second;

  print "Enter the operator (+ or *): ";
  my $op = <STDIN>;
  chomp $op;
  
  if ($op =~ /^[+*]$/)
    {print "$first $op $second = " . eval ("$first $op $second") . "\n";}
  else
    {
    print "$op is neither + nor *.\n";
    next;
    }
  }