private static string GetDayNumberSuffix(int DayNumber /* = 1..31 */) { Debug.Assert(DayNumber >= 1 && DayNumber <= 31); int DayNumber10 = DayNumber % 10; if (DayNumber10 == 1) { if (DayNumber/*%100*/ != 11) return "st"; } else if (DayNumber10 == 2) { if (DayNumber/*%100*/ != 12) return "nd"; } else if (DayNumber10 == 3) { if (DayNumber/*%100*/ != 13) return "rd"; } return "th"; }