using System;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Calculator");

        Console.WriteLine("Enter number:");

        decimal num1 = Convert.ToDecimal(Console.ReadLine());

        Console.WriteLine("Select a operator:");

        Console.WriteLine(" [+] Plus ");

        Console.WriteLine(" [-] Minus");

        Console.WriteLine(" [*] Multiply");

        Console.WriteLine(" [/] Divide");

        Console.WriteLine("");

        string op = Console.ReadLine();

        Console.WriteLine("Enter number:");

        decimal num2 = Convert.ToDecimal(Console.ReadLine());

        Console.WriteLine("Answer:");

        Console.WriteLine(Calculator(num1, num2, op));

    }

​

    public static decimal Calculator(decimal num1, decimal num2, string op)

    {

        string[] operators = {"-", "+", "*", "/"};

        if (Array.Exists(operators, x => x.Equals(op)))

        {

            switch (op)

            {

                case "+":

                    return num1 + num2;

                case "-":

                    return num1 - num2;

                case "*":

                    return num1 * num2;

                case "/":

                    return num1 / num2;

                default:

                    return 0;

            }

        }

        else

        {

            throw new Exception("Invalid operator selected!");

        }

    }

}