add query string to url

I wish to add Query string to current url of site when i click on button. I dont know how its done in SharePoint but know how to do in asp.net like below

string url = HttpContext.Current.Request.Url.AbsoluteUri;
        var uriBuilder = new UriBuilder(url);
        var query = HttpUtility.ParseQueryString(uriBuilder.Query);
        query["Myparam"] = "test";
        uriBuilder.Query = query.ToString();
        url = uriBuilder.ToString();
        Response.Redirect(url);

Update1

I tried below code in selectedIndexChange event of option button

  protected void RadioButtonList_SelectedIndexChanged(object sender, EventArgs e)
    {

        Page.ClientScript.RegisterStartupScript(GetType(), "test",
            "<script type=\"text/javascript\">AddQueryString('" +
            RadioButtonList.SelectedValue).ToString() + "');</script>)");
    }

Then in .ascx file i wrote below

<script type="text/javascript">
function AddQueryString(querystring) {

           SP.SOD.executeFunc("SP.js", "SP.ClientContext", function()    
    {    
        SP.Utilities.UrlBuilder.replaceOrAddQueryString(window.location.href, "param1", querystring);

   });
}</script>

But its not updating url With Query string. Why? I have checked that there are no errors in console and code executes sucessfully.