简单的C#Windows 窗体编程，计算圆的周长、面积与体积。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace AreaOf_Circle
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();//窗体初始化
        }

        private void label2_Click(object sender, EventArgs e)
        {

        }

        private void textBox2_TextChanged(object sender, EventArgs e)
        {
        }
        private void Form1_Load(object sender, EventArgs e)
        {
        }

        private void button1_Click(object sender, EventArgs e)
        {
            double r, l, s, v;
            r = Convert.ToSingle(textBox1.Text);//获取输入半径
            l = Math.PI * 2 * r;//计算周长
            s = Math.PI * r * r;//计算面积
            v = Math.PI * 3.0 / 4.0 * r * r * r;//计算体积
            textBox2.Text = Convert.ToString(l);//显示周长
            textBox3.Text = Convert.ToString(s);//显示面积
            textBox4.Text = Convert.ToString(v);//显示体积
        }

        private void button2_Click(object sender, EventArgs e)
        {
            Application.Exit();//退出
        }
    }
}