using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace PI{    class Program    {        static void Main(string[] args)        {            const Double PI=3.1415926;            Console.WriteLine("请输入圆的半径:");            float r = Convert.ToInt32(Console.ReadLine());            double s =PI * (r * r);            Console.WriteLine("圆的半径是{0}，面积是：{1}",r,s.ToString("0.000"));//限制输出的位数            Console.ReadKey();        }    }}