Grid view Total

<asp:GridView ID="gv" runat="server" ShowFooter="true">
                    </asp:GridView>

protected override void OnInit(EventArgs e)
    {
        base.OnInit(e);
        gv.RowDataBound += new GridViewRowEventHandler(gv_RowDataBound);
    }
    double sum = 0;
    protected void gv_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            sum += Convert.ToDouble(e.Row.Cells[0].Text);
        }
        if (e.Row.RowType == DataControlRowType.Footer)
        {
            e.Row.Cells[0].Text = sum + "";
        }
    }