private void btnThoat_Click(object sender, EventArgs e)
        {
            frmQLMay frm = new frmQLMay();

            frm.Show();
            this.Hide();
        }
        private void btn_QLMay_Click(object sender, EventArgs e)
        {
            frmQLMay frm;

            if (user.TenUser != "")
            {
                frm = new frmQLMay(user);
            }
            else
            {
                frm = new frmQLMay();
            }

            frm.Show();
        }