public static PHAN_SO Tinh(BIEU_THUC P) { PHAN_SO kq; kq = P.So_hang[0]; for (int i = 1; i < P.So_hang.GetLength(0); i++) { if (P.Toan_tu[i - 1] == TOAN_TU.Cong) { kq = XL_PHAN_SO.Tong(kq, P.So_hang[i]); } else if (P.Toan_tu[i - 1] == TOAN_TU.Tru) { kq = XL_PHAN_SO.Hieu(kq, P.So_hang[i]); } } return(kq); }