using System;

​

public class Calculator

{

    protected double result; // Calculation's result

​

    public double Result

    {

        get { return result; }

    }

​

    public virtual void Calculate(double num1, double num2)

    {

        // The base way of calculation, which derived classes can override.

    }

}

​

public class addcalcu : Calculator

{

    public override void Calculate(double num1, double num2)

    {

        result = num1 + num2;

    }

}

​

public class subtractcalcu : Calculator

{

    public override void Calculate(double num1, double num2)

    {

        result = num1 - num2;

    }

}

​

public class dividecalcu : Calculator

{

    public override void Calculate(double num1, double num2)

    {

        if (num2 != 0)

            result = num1 / num2;

        else

            Console.WriteLine("Error: Division by zero!");

    }

}

​

public class multiplycalcu : Calculator

{

    public override void Calculate(double num1, double num2)

    {

        result = num1 * num2;

    }

}

​

public class Program

{

    public static void Main(string[] args)

    {

        double num1, num2;

​

        Console.WriteLine("Enter the first digit:");

        double.TryParse(Console.ReadLine(), out num1);

​

        Console.WriteLine("Enter the second digit:");

        double.TryParse(Console.ReadLine(), out num2);

​

        Calculator calculator;

​

        Console.WriteLine("Choose an operation");

        Console.WriteLine("[1] Addition");

        Console.WriteLine("[2] Subtraction");

        Console.WriteLine("[3] Division");

        Console.WriteLine("[4] Multiplication");

​

        int choice;

        int.TryParse(Console.ReadLine(), out choice);

​

        switch (choice)

        {

            case 1:

                calculator = new addcalcu();

                calculator.Calculate(num1, num2);

                Console.WriteLine("Total: " + calculator.Result);

                break;

            case 2:

                calculator = new subtractcalcu();

                calculator.Calculate(num1, num2);

                Console.WriteLine("Total: " + calculator.Result);

                break;

            case 3:

                calculator = new dividecalcu();

                calculator.Calculate(num1, num2);

                Console.WriteLine("Result: " + calculator.Result);

                break;

            case 4:

                calculator = new multiplycalcu();

                calculator.Calculate(num1, num2);

                Console.WriteLine("Total: " + calculator.Result);

                break;

            default:

                Console.WriteLine("Invalid choice!");

                break;

        }

    }

}