protected void btnCalcular_Click(object sender, EventArgs e)
        {
            try
            {
                double      radio      = Convert.ToDouble(txtRadio.Text);
                double      altura     = Convert.ToDouble(txtAltura.Text);
                WebService1 webService = new WebService1();

                txtArea.Text = webService.Cilindro(radio, altura).ToString();
                webService   = null;
                return;
            }
            catch (Exception error)
            {
                labelMsg.Text = error.Message;
                return;
            }
        }