2.输入宽和高，计算面积

      

  private void button11_Click(object sender, EventArgs e)
        {
            string 长 = textBox1.Text;
            string 宽 = textBox2.Text;
            int i1,i2;
            if (int.TryParse(长, out i1) == false)
            {
                MessageBox.Show("输入不合法！");
            }
            if (int.TryParse(宽, out i2) == false)
            {
                MessageBox.Show("输入不合法！");
            }
            int i3 = i1 * i2;
            textBox3.Text = Convert.ToString(i3);
        }