Why should i write code in html form

Following is the code that i wrote in asp.net , please i want to know can i write this code in .cs file? because i didnt find it how to write? any one can help me ?

<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" DataKeyNames="ProductID"
DataSourceID="SqlDataSource2">
<Columns>
<asp:CommandField ShowEditButton="True" />
<asp:TemplateField HeaderText="ProductName" SortExpression="ProductName">
<EditItemTemplate>
<%-- <asp:TextBox ID="TextBox1" runat="server" Text='<%# Bind("ProductName") %>'></asp:TextBox>--%>
<asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="SqlDataSource2"
DataTextField="ProductName" DataValueField="ProductName" SelectedValue='<%# Bind("ProductName") %>'>
</asp:DropDownList><asp:SqlDataSource ID="SqlDataSource2" runat="server" ConnectionString="<%$ ConnectionStrings:NorthwindConnectionString %>"
SelectCommand="SELECT [ProductName] FROM [Products]"></asp:SqlDataSource> </EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("ProductName") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="QuantityPerUnit" HeaderText="QuantityPerUnit" SortExpression="QuantityPerUnit" />
<asp:BoundField DataField="UnitsOnOrder" HeaderText="UnitsOnOrder" SortExpression="UnitsOnOrder" />
<asp:CheckBoxField DataField="Discontinued" HeaderText="Discontinued" SortExpression="Discontinued" />
<asp:BoundField DataField="ProductID" HeaderText="ProductID" InsertVisible="False"
ReadOnly="True" SortExpression="ProductID" />
</Columns>
</asp:GridView>

This article provides a brief overview of the code-behind model

ASP.NET Code-Behind Model Overview

http://support.microsoft.com/kb/303247

hope it helps!