C#程序设计---->计算圆面积windows程序

值得说的就是添加一个回车事件，

http://blog.csdn.net/nanwang314/article/details/6176604

private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
     {
           if(e.KeyCode==Keys.Enter)
           {
                 MessageBox.Show("您在textBox1里按下了回车键");
           }
     } 

　　这个样子就可以添加一个回车事件…………

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 CircleAreaW
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            double r;
            r = double.Parse(txtR.Text);
            MyCircle aCircle = new MyCircle(r);


            double aArea = aCircle.CircleArea();
            dblArea.Text = aArea.ToString("f4");
        }

        private void txtR_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Enter)
            {
                MessageBox.Show("您在textBox1里按下了回车键");

                double r;
                r = double.Parse(txtR.Text);
                MyCircle aCircle = new MyCircle(r);


                double aArea = aCircle.CircleArea();
                dblArea.Text = aArea.ToString("f4");
            }
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace CircleAreaW
{
    class MyCircle
    {
        double circleR;
        public MyCircle(double dblR)
        {
            circleR = dblR;
        }
        public double CircleArea()
        {
            double dblArea = Math.PI * circleR * circleR;
            return dblArea;
        }
    }
}