窗体应用程序

private void button1_Click(object sender, EventArgs e)

{

double r;

r = Convert.ToInt32(textBox1.Text);

textBox2.Text = Convert.ToString(2 * r * System.Math.PI);

textBox3.Text = Convert.ToString(r * r * System.Math.PI);

textBox4.Text = Convert.ToString(r * r * r * 4 / 3 * System.Math.PI);

}