factorial

 server----

public long factorial(int number)
        {
            if (number == 0)
                return 1;
            else
                return (number * factorial(number - 1));
        }

client------

            int c1 = Convert.ToInt32(TextBox1.Text);
            ServiceReference1.WebService1SoapClient obj = new ServiceReference1.WebService1SoapClient();
            long res = obj.factorial(c1);
            Label2.Text = Convert.ToString(res);