confirm dilog box in c# code window

ScriptManager.RegisterStartupScript(this, this.GetType(), "ajax", "<script language="javascript">if(confirm('Do u wanna change?')){ //do somthing } else { //do smthing } </script>", false)

try this

hi
you can try my code for displaying and processing using javascript.

<script language ="javascript" >
    function delval() {
        if (confirm("Do you want to delete")) {
            $.post("default16.aspx?action=delete", { id: "4" }, function (data) {
                //show results in tags
            });
        }
        else {
           //do nothing
        }
    }
</script>

And for your requirement you can not interrupt processing untill second request comes

Because every request from user serves as a new request.
we can not wait response from that confirm msg

Use Jquery to check confirm msg it'll get best experience to you for achieving your requirement.

All the Best

try with fillowing code

<asp:Button runat="server" ID="Save" OnClientClick="if (!confirm('Are you sure?')) return false;" />