Function SongayTrongthang(Thang As Long, Nam As Long) As Byte
Select Case Thang
Case 1, 3, 5, 7, 8, 10, 12: SongayTrongthang = 31
Case 4, 6, 9, 11: SongayTrongthang = 30
Case 2
Select Case Nam
Case (Nam Mod 4 = 0 And Nam Mod 100 = 0) Or Nam Mod 400 = 0: SongayTrongthang = 29
Case Else: SongayTrongthang = 28
End Select
End Select
End Function