using System;

public class Program

{

    static int primaryNum = new Int32();

    static int secondaryNum = new Int32();

        static int Addition(int numeral1, int numeral2)

    {

        return numeral1 + numeral2;

    }

    static int Subtraction(int numeral1, int numeral2)

    {

        return numeral1 - numeral2;

    }

    static int Multiplication(int numeral1, int numeral2)

    {

        return numeral1 * numeral2;

    }

    static int Division(int numeral1, int numeral2)

    {

        return numeral1 / numeral2;

    }

    public static void Main()

    {

        string parsingNum = null;

        Console.WriteLine("Welcome to Cameron's first calculator");

        bool validEntry = true;

        while (validEntry)

        {

            Console.Write("Enter a whole number: ");

            parsingNum = Console.ReadLine();

            if (Int32.TryParse(parsingNum, out primaryNum))

            {

                validEntry = false;

            }

            else

            {

                Console.WriteLine("Invalid entry");

            }

        }

        validEntry = true;

        while (validEntry)

        {

            Console.Write("Enter another whole number: ");

            parsingNum = Console.ReadLine();

            if (Int32.TryParse(parsingNum, out secondaryNum))

            {

                validEntry = false;

            }

            else

            {

                Console.WriteLine("Invalid entry");

            }

        }

        validEntry = true;

        while (validEntry)

        {   

            string entry = null;

            string[] validChoice = { "A", "S", "M", "D" }; 

            int answer = new Int32();

            Console.WriteLine("Choose an operation and press enter: (A)ddition, (S)ubtraction,  (M)ultiplication, (D)ivision ");

            entry = Console.ReadLine();

            if (entry.Equals(validChoice[0], StringComparison.OrdinalIgnoreCase))

            {

                answer = Addition(primaryNum, secondaryNum);

                Console.WriteLine(primaryNum + " + " + secondaryNum + " = " + answer);

                break;

            }

            else if (entry.Equals(validChoice[1], StringComparison.OrdinalIgnoreCase))

            {

                answer = Subtraction(primaryNum, secondaryNum);

                Console.WriteLine(primaryNum + " - " + secondaryNum + " = " + answer);

                break;

            }

            else if (entry.Equals(validChoice[2], StringComparison.OrdinalIgnoreCase))

            {

                answer = Multiplication(primaryNum, secondaryNum);

                Console.WriteLine(primaryNum + " x " + secondaryNum + " = " + answer);

                break;

            }

            else if (entry.Equals(validChoice[3], StringComparison.OrdinalIgnoreCase))

            {

                answer = Division(primaryNum, secondaryNum);

                Console.WriteLine(primaryNum + " / " + secondaryNum + " = " + answer);

                break;

            }

            else

            {

                Console.WriteLine("Invalid entry");

            }

        }

    }

​

}