using System;

​

namespace VietJackCsharp

{

    class TestCsharp

    {

        public static void Main()

        {

​

            double r, chu_vi, dien_tich;

            double PI = 3.14;

            Console.Write("Nhap ban kinh duong tron: ");

            r = Convert.ToDouble(Console.ReadLine());

            chu_vi = 2 * PI * r;

            Console.WriteLine("\nChu vi duong tron la: {0}", chu_vi);

            dien_tich = PI * r * r;

            Console.WriteLine("Dien tich duong tron la: {0}", dien_tich);

            Console.Read();  

​

            Console.ReadKey();

        } 

    }

}

static void Main(string[] args)

        {

            int N;

            Console.WriteLine("nhap vao N:");

            N = Convert.ToInt32(Console.ReadLine());

            int T=1;

            tinhtich(T, N);

            Console.ReadKey();

        }

        static int tinhtich(int x, int  y)

        {

            for (int i = 1; i <= y;i+=2)

            {

                x = x * i;

            }

            Console.WriteLine("Tich la:{0}", x);

            return x;

        }

    }

}