how to delete multiple item using checkbox in gridview control?

Question

hello i want to delete multiple item using checkbox in gridview control ..
 
here is my code:

 

 
<asp:GridView ID="GridView1" runat="server" AllowPaging="True" 
AutoGenerateColumns="False"
BackColor="White" BorderColor="#999999" BorderStyle="None" BorderWidth="1px"
CellPadding="2" DataKeyNames="code" DataSourceID="SqlDataSource1"
OnRowCancelingEdit="GridView1_RowCancelingEdit" 
OnRowEditing="GridView1_RowEditing" 
OnRowUpdating="GridView1_RowUpdating" 
GridLines="Vertical"
OnRowDeleting="GridView1_RowDeleting" Width="200px">
<FooterStyle BackColor="#CCCCCC" ForeColor="Black" />
<RowStyle BackColor="#EEEEEE" ForeColor="Black" />
<Columns>
<asp:TemplateField HeaderText="Item">
<ItemTemplate>
<asp:Image ID="Image1" runat="server" ImageUrl='<%# Eval("purl", "items/{0}") %>' />
</ItemTemplate>
<ControlStyle Height="100px" Width="100px" />
</asp:TemplateField>
<asp:TemplateField HeaderText="Product Code" SortExpression="Product Code">
<ItemTemplate>
<asp:Label ID="lblcode" runat="server" Text='<%# Bind("code") %>'/>
</ItemTemplate>
<ControlStyle Width="20px" />
</asp:TemplateField>
<asp:TemplateField HeaderText="Product Name" SortExpression="Product Name">
<ItemTemplate>
<asp:Label ID="lblpname" runat="server" Text='<%# Bind("pname") %>'/>
</ItemTemplate>
<ControlStyle Width="120px" />
</asp:TemplateField>
<asp:TemplateField HeaderText="Price" SortExpression="Price">
<ItemTemplate>
<asp:Label ID="lblprice" runat="server" Text='<%# Bind("price") %>'/>
</ItemTemplate>
<ControlStyle Width="100px" />
</asp:TemplateField>
<asp:TemplateField HeaderText="Quantity" SortExpression="Quantity">
<EditItemTemplate>
<asp:TextBox ID="txtqty" runat="server" Text='<%# Bind("qty") %>'/>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="lblqty" runat="server" Text='<%# Bind("qty") %>'/>
</ItemTemplate>
<ControlStyle Width="20px" />
</asp:TemplateField>
<asp:TemplateField HeaderText="Total" SortExpression="Total">
<ItemTemplate>
<asp:Label ID="lbltot" runat="server" Text='<%# Bind("tot") %>'/>
</ItemTemplate>
<ControlStyle Width="100px" />
</asp:TemplateField>
<asp:CommandField ButtonType="Button" ShowDeleteButton="True" ShowEditButton="True"
ShowSelectButton="True" HeaderText="Update" >
<ControlStyle Width="50px" />
<ItemStyle Width="20px" />
</asp:CommandField>
<asp:TemplateField HeaderText="check">
<EditItemTemplate>
<asp:CheckBox ID="CheckBox1" runat="server" />
</EditItemTemplate>
<ItemTemplate>
<asp:CheckBox ID="CheckBox1" runat="server" />
</ItemTemplate>
<ControlStyle Width="10px" />
</asp:TemplateField>
</Columns>
<PagerStyle ForeColor="Black" HorizontalAlign="Center" BackColor="#999999" />
<SelectedRowStyle BackColor="#008A8C" Font-Bold="True" ForeColor="White" />
<HeaderStyle BackColor="#000084" Font-Bold="True" ForeColor="White" />
<AlternatingRowStyle BackColor="Gainsboro" />
</asp:GridView>
<br /><br /></center> 
<div align="right">
<asp:Label ForeColor="white" ID="lblt" Text="Total:" Font-Bold="True" Font-Size="X-Large" Width="108px" runat="server"/>
<asp:Label CssClass="lbl1" ForeColor="White" ID="lbltot" Text="" runat="server" Font-Bold="True" Font-Size="X-Large" Width="108px"/>
</div>
<br /><br /><br /><br />
<asp:Button ID="final" runat="server" Text="Final Purchase" OnClick="final_Click" /> 
<br />
<br />
<br />
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>"
SelectCommand="SELECT purl,code,pname,price,qty,(qty*price)as tot FROM [tmp]"
UpdateCommand="UPDATE [tmp] set
[qty] =@qty 
WHERE [code] = @code" DeleteCommand="delete tmp where code='@code'">

<UpdateParameters>
<asp:Parameter Name="qty" Type="Int32" /> 
<asp:Parameter Name="code" Type="String" />
</UpdateParameters>
<DeleteParameters>
<asp:Parameter Name="code" Type="string" />
</DeleteParameters>
</asp:SqlDataSource>