private void btnThem_Click(object sender, EventArgs e)
{
btnLuu.Visible = true;
btnhuy.Visible = true;
btnThem.Visible = false;
btnSua.Visible = false;
btnXoa.Visible = false;
hien();
txtSoLuongHS.ReadOnly = true;
ktluu = 2;
DataTable maxid = new DataTable();
maxid = LopDAO.MaxIDLop();
int idlop;
try
{
idlop = (int)maxid.Rows[0][0];
}
catch
{
idlop = 0;
}
idlop++;
txtIDLop.Text = idlop.ToString();
int soluong = 0;
txtSoLuongHS.Text = soluong.ToString();
}