public string GetMaHoaDonNext(int congThem = 0) { string lastNumString = dal_hoaDon.GetMaHoaDonLast(); string lastNumStringRemove = lastNumString.Remove(0, 2); //Lay phan so ra int lastNum = Int32.Parse(lastNumStringRemove); int nextNum = lastNum + 1 + congThem; string nextNumString = nextNum.ToString(); while (nextNumString.Length < 8)// gom 8 so { nextNumString = "0" + nextNumString; } return("HD" + nextNumString); }