Question

I have to give textbox control id like below

 <asp:TextBox ID="7_1" runat="server">

It is not allowing me. If I give

<asp:TextBox ID="Test7_1" runat="server">

Then it works fine. Why? Why can not give start with numbers?

Answer 1

Because in .NET variable names cannot start with a number. Neither an id in HTML by the way. So when Visual Studio tries to generate a .designer file from the aspx page it chokes because this is invalid:

protected TextBox 7_1;

it simply cannot compile.