using System;

using System.Linq;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        string input = "";

        int numCheck = 0;

        Regex whiteList = new Regex("^[1234567890]+$");

        do

        {

            numCheck = 0;

            Console.Write("Please input the two numbers you wish to use seperated by a space: ");

            input = Console.ReadLine();

            var numbers = input.Split(new []{' '}, StringSplitOptions.RemoveEmptyEntries);

            if (numbers.Length != 2 || !numbers.All(num => whiteList.IsMatch(num)))

            {

                Console.WriteLine("You entered " + input + " You did not enter two numbers seperated by a space, please try again.");

                numCheck = 1;

            }

        }

        while (numCheck == 1);

    }

}