DigitToText

class DigitToText
{
    static void Main()
    {
        System.Console.WriteLine(DigitToString(123456789));
    }

    static string DigitToString(long value_to_convert)
    {
        long order_of_number = 10;
        string to_text = "";
        string[] text_nums = { "нуль", "один", "два", "три", "четыре", "пять", "шесть", "семь", "восемь", "девять" };
        while ((value_to_convert / (order_of_number / 10)) > 0)
        {
            to_text = to_text.Insert(0, text_nums[(value_to_convert % order_of_number) / (order_of_number / 10)] + " ");
            order_of_number *= 10;
        }
        return to_text;
    }
}