How do I calculate in grideview

See more:

ASP.NET

I am trying to make an order form. when a code is selected from drop down list in grid view then it automatically show Name and Price in label. But when a value is given in the Quantity text box it does not work. All data come from a different table. My grid view is look like...

<asp:GridView ID="GridView1" runat="server">
    <columns>
         <asp:TemplateField HeaderText="Code" >
             <itemtemplate>
                 <asp:DropDownList ID="ddlCode" runat="server">
             </itemtemplate>                                                                      
          
        <asp:TemplateField HeaderText="Name" >
             <itemtemplate>
                 <asp:Label ID="lblName" runat="server" />    
             </itemtemplate>                                                                      
          
        <asp:TemplateField HeaderText="Price" >
             <itemtemplate>
                 <asp:Label ID="lblPrice" runat="server" />    
             </itemtemplate>                                                                      
          
        <asp:TemplateField HeaderText="Quantity" >
             <itemtemplate>
                 <asp:TextBox ID="txtQuantity" runat="server">
             </itemtemplate>                                                                      
    </columns>

How do I calculate Total and all rows Total ?