private void buttonSua_Click(object sender, EventArgs e)
{
monhocbus.SuaMonHoc(textBoxMaMon.Text, textBoxTenMon.Text, comboMaKhoa.SelectedItem.ToString());
dataGridViewDS_MH.DataSource = monhocbus.XemTatCaMonHoc();
textBoxTongSo.Text = (dataGridViewDS_MH.RowCount).ToString();
}
