How can I take/catch dynamic parameter(in form of querystring) into .cs file

Hello I came up with situation where I am taking value from user in the form of querystring.

Ex: sitename/sample.aspx?username=''&userid=''

cs file

string Username = "";
if (Request.QueryString["username"] != null)
Username = Request.QueryString["username"].ToString();
string userid = "";
if (Request.QueryString["userid"] != null)
userid = Request.QueryString["userid"].ToString();

Name of first 2 parameter is fix,so name name of querystring is fix.After these 2 parameter,user may enter or may not enter any parameter.Parameter count can be from 1 to many and vary in datatype.

Ex: sitename/sample.aspx?username=''&userid=''&Date=
Ex: sitename/sample.aspx?username=''&userid=''&Date=&amount=

how can I take/catch dynamic parameter into .cs file?