private void btnCapnhat_Click(object sender, EventArgs e)
{
DataGridViewRow row = dataGridViewNguoiDung.CurrentRow;
string maso = row.Cells["colmaso"].Value.ToString();
string username = row.Cells["colusername"].Value.ToString();
string loaitaikhoancol = row.Cells["colquyen"].Value.ToString();
data.UpdateNguoiDung(username, loaitaikhoancol, maso);
loadNguoiDung();
}