while (@ARGV){
  if ($ARGV[0] =~ /add/) {
       $rtn = add($ARGV[1], /.../);
       print "The sum is: $rtn";
    }

    elsif ($ARGV[0] =~ /multiply/) {
       $rtn = multiply($ARGV[1], /.../);
       print "The product is: $rtn";
    }


sub add {
     $sum = $sum + $ARGV;
    return $sum;
  }

sub multiply {
     $product = $product * $ARGV;
	 return $product;
  }
}