How to set ID for Buttons in asp.net dynamically? - asp.net

Question

I wrote this code for set id for buttons by reading a field from db connected to sqldatasource,but the error say that I can set id like ID="btn1". but this is static. what should I do?
<asp:Button ID='<%# Eval("num") %>' runat="server" cssclass=btnd OnClick="delete_kala" />
this code is in datalist connected to sqldatasource.
codes for reading data from db:
<table class="cart-table">
<tr>
<td width=450>
<asp:Label ID="kalanameLabel" runat="server" Text='<%# Eval("kalaname") %>'/>
<asp:Label ID="kaladetailLabel" runat="server" Text='<%# Eval("kaladetail") %>'/>
<br />
</td>
<td width=100>
<asp:Label ID="kalapriceLabel" runat="server" Text='<%# Eval("kalaprice") %>' ForeColor=Green />
<asp:Label ID="Label1" runat="server" Text='تومان' />
<br />
</td>
<td>
<asp:Label ID="numLabel" runat="server" Text='<%# Eval("num") %>' />
<asp:Label ID="Label2" runat="server" Text='عدد' />
<br />
</td>
<td>
<asp:Button ID='<%# Eval("num") %>' runat="server" cssclass=btnd OnClick="delete_kala" />
<%-- <img src="images/delete.png" width="20" height=20 /> --%>
<br> </br></td>
<td>
<asp:Button ID="ed" runat="server" cssclass=btne OnClick="edit_kala"/>
<%-- <img src="images/edit.png" width=20 height=20 /> --%>
<br> </br></td>
</tr>
</table>
</ItemTemplate>
</asp:DataList>
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
ConnectionString="<%$ ConnectionStrings:onlineshopConnectionString %>" SelectCommand="
SELECT userid, kalaidbuy, num,kalaname,kaladetail,kalaprice
FROM cart inner join kala on
cart.kalaidbuy=kala.kalaID
where userid=#d "
>
<SelectParameters>
<asp:QueryStringParameter Name="d" QueryStringField="UID" />
</SelectParameters>
</asp:SqlDataSource>