private void btnKH_Click(object sender, EventArgs e)
{
dgvKhachHang.DataSource = kh.Show10KH();
int i = 0;
while (i < dgvKhachHang.Rows.Count - 1)
{
dgvKhachHang.Rows[i].Cells[0].Value = (i + 1).ToString();
i++;
}
}
