Get the index of the SelectedRow in a DataGridView

private void dataGridView1_SelectionChanged(object sender, EventArgs e)
{

if (dataGridView1.SelectedRows.Count == 1)
{
     txttextbox1.Text = dataGridView1.Rows[dataGridView1.SelectedRows[0].Index].Cells["CustCode"].Value.ToString();
}
}