Looping thru gridview rows

I want to loop thru the rows in my gridview.  Here is my code:
<asp:GridView id="gvOrderLines" runat="Server" DataKeyNames="OrderLineId" AutoGenerateColumns="False"> <Columns> <asp:TemplateField Visible="false"> <ItemTemplate> <asp:Label id="lblOrderLineId" runat="server" Text='<%# Eval("OrderLineId") %>' > </asp:Label> </ItemTemplate> </asp:TemplateField> <asp:TemplateField Visible="false"> <ItemTemplate> <asp:Label id="lblOrderId" runat="server" Text='<%# Eval("OrderId") %>' > </asp:Label> </ItemTemplate> </asp:TemplateField> <asp:TemplateField HeaderText="Line Number" SortExpression="LineNum" HeaderStyle-HorizontalAlign="Left& ...