private void btThemLop_Click(object sender, EventArgs e) { try { int maHS = Convert.ToInt32(tbMaHs.Text); int maLop = Convert.ToInt16(cbLop.SelectedValue.ToString()); HocSinhDAL hsDAL = new HocSinhDAL(); hsDAL.ThemHSLop(maHS, maLop); HienThiDSLop(); } catch { } }