Standard Calculator Using Switch & While

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

namespace ConsoleApplication14
{
    class Program
    {
        static void Main(string[] args)
        {
            //calculator
            string exit = ".";
            while (exit != "exit" && exit != "close")
            {
                Console.WriteLine("Enter two numbers:");
                double num1 = double.Parse(Console.ReadLine());
                double num2 = double.Parse(Console.ReadLine());
                Console.WriteLine("Please choose operator (*, /, +, -):");
                string op = Console.ReadLine();
                switch (op)
                {
                    case ("*"):
                        Console.WriteLine(num1 * num2);
                        break;

                    case ("/"):
                        Console.WriteLine(num1 / num2);
                        break;

                    case ("+"):
                        Console.WriteLine(num1 + num2);
                        break;

                    case ("-"):
                        Console.WriteLine(num1 - num2);
                        break;

                    default:
                        Console.WriteLine("Invalid operator!");
                        break;
                }
                Console.WriteLine("Type 'exit' or 'close' in order to exit the program. If you would like to\nchoose again, press enter.");
                exit = Console.ReadLine();
                Console.WriteLine();
            }
        }
    }
}