实例4_2 类的属性

题目描述  

求圆的面积。

控件	属性	属性设置	控件	属性	属性设置
label1	Text	半径：	txtBox1	Name	txtRadius
button1	Name	btnCalculate	label2	Name	lblShow
	Text	计算		Text	" "

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

namespace Test4_2
{
    public partial class Test4_2 : Form
    {
        public Test4_2()
        {
            InitializeComponent();
        }

        private void btnCalculate_Click(object sender, EventArgs e)
        {
            Circle circle = new Circle();
            circle.Radius = Convert.ToDouble(txtRadius.Text);
            lblShow.Text = string.Format("半径为{0}的圆的面积为{1}",circle.Radius,circle.Area);
        }
        class Circle
        {
            const double pi=3.1415926;
            private double radius;
            public double Radius
            {
                get { return radius; }
                set
                {
                    if (value < 0) radius = 0;
                    else radius = value;
                }
            } 
                public double Area
                {
                    get{return pi*Radius*Radius;}
                }
        }
    }
}