private void btn_giam_Click(object sender, EventArgs e) { if (cbo_lau.SelectedIndex > -1) { //index = comboBox1.SelectedIndex; //MessageBox.Show(dtchuatinh.Rows[index]["SoLuong"].ToString()); //MaNV = cls_Main.MaNV; MaHD = mahd; MaMon = cbo_lau.SelectedValue.ToString(); if (bd.GiamMon(ref err, MaHD, MaMon)) { laydulieuhangdangban(MaHD); } } }