<%@ Page Language="C#" %>

<script runat="server">
    void b1_c(object sender, EventArgs e)
    {
    l1.Text="!!!";
    }
</script>
<form runat="server">
    <asp:Button runat="server" id="b1" onclick="b1_c" Text="bum"/>
    <asp:Label runat="server" id="l1"/>
</form>