using System;

public class Program

{

        public static void Main(string[] args)

        {

            Console.Write("1st num:");

            double num1 = Convert.ToDouble(Console.ReadLine());

​

            Console.Write("Function:");

            string op = Console.ReadLine();

​

            Console.Write("2nd num:");

            double num2 = Convert.ToDouble(Console.ReadLine());

​

            if (op == "+")

            {

                Console.WriteLine(addition(num1, num2));

            }

            else if (op == "-")

            {

                Console.WriteLine(subtract(num1, num2));

            }

            else if (op == "*")

            {

                Console.WriteLine(multiply(num1, num2));

            }

            else if (op == "/")

            {

                Console.WriteLine(divide(num1, num2));

            }

            else

            {

                Console.WriteLine("Invalid Operator");

            }

        }

        public static double addition(double a, double b)

        {

            return a + b;

        }

        public static double subtract(double a, double b)

        {

            return a - b;

        }

        public static double multiply(double a, double b)

        {

            return a * b;

        }

        public static double divide(double a, double b)

        {

            return a / b;

        }

    }

​