C# 函数重载 示例 求圆的面积

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

namespace ConsoleApplication
{
    class Circle
    {
       
        private const float PI = 3.141526F;

        //1.没有任何已知条件
        public static double Area()
        { 
            Console.WriteLine("空空如也！");
            return 0;
        
        }
        //2.已知圆心坐标
        public static double Area(int x1, int y1)
        {
            Console.WriteLine("这是一个圆点，坐标为({0},{1})",x1,y1);
            return 0;
        }
        //3.已知半径
        public static double Area(double r)
        {
            double theArea;
            theArea = PI * r * r;
            return theArea;

        }
        //4.已知圆心坐标和半径
        public static double Area(int x1, int y1, double r)
        {
            Console.WriteLine("这是一个圆点在({0},{1})半径为{2}的圆", x1, y1, r);
            return Area(r);
        
        }
        //5.已知圆心和圆周边上的一点
        public static double Area(int x1, int y1, int x2, int y2)
        {
            int x = x2 - x1;
            int y = y2 - y2;
            double r = (double)Math.Sqrt(x*x+y*y);
            Console.WriteLine("这是一个圆心在({0},{1}),圆周边一点在({2},{3})的圆，圆的半径为{4}",x1,y1,x2,y2,r);
            return Area(r);
        
        }
        static void Main(string[] args)
        {
            int x1=2,x2=4;          //x坐标
            int y1=3,y2=5;          //y坐标
            double radius=3;        //半径
            double CircleArea = 0;
            CircleArea = Area();
            Console.WriteLine("-->1.面积为{0}",CircleArea);
            Console.WriteLine();

            CircleArea = Area(x1,y1);
            Console.WriteLine("-->2.面积为{0}", CircleArea);
            Console.WriteLine();

            CircleArea = Area(radius);
            Console.WriteLine("-->3.面积为{0}", CircleArea);
            Console.WriteLine();

            CircleArea = Area(x1, y1, radius);
            Console.WriteLine("-->4.面积为{0}", CircleArea);
            Console.WriteLine();

            CircleArea = Area(x1, y1, x2, y2);
            Console.WriteLine("-->5.面积为{0}", CircleArea);
            Console.WriteLine();

            Console.ReadKey();

        }
       
    }
}

来源：https://www.cnblogs.com/zhangzufa/archive/2009/04/01/1427370.html