有关圆的计算。

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

namespace 运算符
{
class Program
{
const double pai = 3.14;
static void Main(string[] args)
{
Console.Write("请输入一个圆的半径r=：");
string str_r= Console.ReadLine();
double banjing=double.Parse ( str_r );
double int_R= banjing * 2;
Console.WriteLine("该圆的直径为R=:{0}" , int_R );
double dou_c =banjing*2*pai ;
Console.WriteLine("该圆的周长为C=：{0}",dou_c );
double dou_s = pai * banjing*banjing ;
Console.WriteLine("该圆的面积为S=:{0}",dou_s);
Console.ReadLine();
}
}
}