string number = "1234567890";
number = number.Replace("1", "один");
number = number.Replace("2", "два");
number = number.Replace("3", "три");
number = number.Replace("4", "четыре");
number = number.Replace("5", "пять");
number = number.Replace("6", "шесть");
number = number.Replace("7", "семь");
number = number.Replace("8", "восемь");
number = number.Replace("9", "девять");
number = number.Replace("0", "ноль");
return number;