C#程序设计---->计算圆面积windows程序

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");
}
}

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;
}
}
}