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

namespace ConsoleApp1
{
    class Program
    {
        public static void Main(string[] args)
        {
            while (true)
            {
                Console.WriteLine("Pick one of these four letters for the calculation.. A: Division, B: Multiplication, C:Additon, D: Subtraction");
                string choice = Console.ReadLine();
                choice.ToLower();

                Console.WriteLine("What is your first number?");
                double first_number;
                Double.TryParse(Console.ReadLine(), out first_number);


                Console.WriteLine("What is your second number?");
                double second_number;
                Double.TryParse(Console.ReadLine(), out second_number);

                if (choice == "b")
                {
                    Console.WriteLine("Your result is: " + Multiplication(first_number, second_number));
                    Console.ReadLine();
                }

                else if (choice == "a")
                {
                    Console.WriteLine("Your result is: " + Division(first_number, second_number));
                    Console.ReadLine();
                }

                else if (choice == "c")
                {
                    Console.WriteLine("Your result is: " + Addition(first_number, second_number));
                    Console.ReadLine();
                }

                else if (choice == "d")
                {
                    Console.WriteLine("Your result is: " + Subtraction(first_number, second_number));
                    Console.ReadLine();
                }

                else
                {
                    Console.WriteLine("Please write in one letter that is listed!");
                }
            }
        }
        static double Multiplication(double first_number, double second_number)
        {
            return first_number * second_number;
        }
        static double Division(double first_number, double second_number)
        {
            return first_number / second_number;
        }
        static double Addition(double first_number, double second_number)
        {
            return first_number + second_number;
        }
        static double Subtraction(double first_number, double second_number)
        {
            return first_number - second_number;
        }
    }
}