How to use query string to find requesting page in ASP.NET?

I have a page signup.aspx where user can register, how this page will find from which page request came from and how it will red开发者_StackOverflowirect user after registration to the requesting page. I want to do this using query string but don't know how

On any links to the register page put

<a href="Signup.aspx?ReturnUrl=<%=Request.Url.AbsolutePath%>">Register Here</a>

then on your register form when they have registered add:

if (!String.IsNullOrEmpty(Request["ReturnUrl"]))
     Response.Redirect(Request["ReturnUrl"]);
else
     Response.Redirect("~/Default.aspx");

if(Request.QueryString["foo"] == "bar"){
    Response.Redirect("page.php", true);
} 

This would get the information from http://www.example.com/registered.aspx?foo=bar

So Request.QueryString["QueryString"] is the value of anything after the ? and each variable after the &. so if you had http://www.example.com/registered.aspx?foo=bar&abc=def

Then you would have 2 querystrings, foo and abc.