using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        foreach (var x in Combinations(2, '0', '9'))        

        {

            Console.WriteLine(x);

        }

    }

​

    public static IEnumerable<char[]> Combinations(int length, char startChar, char endChar)

    {

        var n = endChar - startChar + 1; 

        var s = new string(startChar, length).ToCharArray();

        for (var i = 1; i <= Math.Pow(n, length); ++i)

        {

            yield return s;

            for (var j = 0; j < s.Length; ++j)

            {

                if (j == 0 || i % Math.Pow(n, j) == 0)

                {

                    s[s.Length - 1 - j] = (char)(startChar + (s[s.Length - 1 - j] - startChar + 1) % n);

                }

            }

        }

    }

}