How row indexing is possible in asp.net grid view.

<asp:GridView>
                                                <Columns>
                                                    <asp:TemplateField headertext="s.no">
                                                        <ItemTemplate>
                                                            <%# Container.DataItemIndex + 1 %>
                                                        </ItemTemplate>
                                                    </asp:TemplateField>
                                                </Columns>
</grid view>

<%=txtUserName.ClientID%>.value