using System;

​

public class Program

{

    public static void Main()

    {

        string choice = "qwertyuiop";

        while (choice != "q" && choice != "q")

        {

            Console.WriteLine("Please enter a double.");

            string userInput = Console.ReadLine();

            double sans;

            if (double.TryParse(userInput, out sans))

            {

                Console.WriteLine("Good job.");

            }

            else

            {

                Console.WriteLine("Error. Please enter a double.");

            }

​

            Console.WriteLine("Restarting program... press q to quit.");

            choice = Console.ReadLine();

        }

    }

}