How to Compare two columns on a gridview and display it in the third?

Question

<asp:TemplateField HeaderText="Amount1">
    <ItemTemplate>
         <asp:TextBox ID="txtAmount1" runat="server"></asp:TextBox>
    </ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Amount2">
    <ItemTemplate>
        <asp:TextBox ID="txtAmount2" runat="server"></asp:TextBox>
    </ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Greater Amount">
    <ItemTemplate>
        <asp:Label ID="lblAmount" runat="server" ></asp:Label>
    </ItemTemplate>
</asp:TemplateField>