static void Main(string[] args) {

            float PI = 3.14f;
            float r;
            Console.Write("Put 1 to Calcuate the Length of the Circle \n");
            Console.Write("Put 2 to Calcuate the Area of the Circle \n");
            Console.Write("you put :");
            string x = Console.ReadLine();
            switch (x) {
                case "1":
                    Console.Write("put radius:");
                    r = int.Parse(Console.ReadLine());
                    float L = (float)2 * PI * r;
                    Console.Write("Lenght of circle is :{0:f}\n", L);
                    break;
                case "2":
                    Console.Write("put radius:");
                    r = int.Parse(Console.ReadLine());
                    float A = (float)PI * (r * r);
                    Console.Write("Area of circle is : {0}\n", A);
                    break;
                default:
                    Console.Write("Error\n");
                    break;
            }
            Console.Write("Press any key to continue");
            Console.ReadKey();
        }