Create querystring dynamic

I need to create the link href dynamically like the link is
abc.com
then i have to add the param like aabc.com/default.aspx?pid=3?test=abc
if it is like this abc.com/
then the href like abc.com/default.aspx?pid=3?test=abc
if the url like abc.com/default.aspx?pid=3?test=abc
the i have to chang the id like abc.com/default.aspx?pid=35?test=abc
 
how to do this .. my site is online and on the local..
...