i want to select select rowIndex of selected gridviewrow

protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
     clear();
     LinkButton myButton = GridView1.SelectedRow.Cells[0].Controls[0] as LinkButton;
     if (myButton != null)
     {
         txtName.Text = myButton.Text;
     }
     txtAddress.Text = GridView1.SelectedRow.Cells[1].Text; ;
     txtEmailId.Text = GridView1.SelectedRow.Cells[2].Text; ;
     txtPhoneNumber.Text = GridView1.SelectedRow.Cells[3].Text; ;
}

protected void btnDelete_Click(object sender, EventArgs e)
{
     //i want to select select rowIndex of selected gridviewrow
}