Functions – Get URL arguments

I have an example link

http: // mysite / login? user_id = 6? reg = true

how to get user_id Y reg form of values $ _GET? Or how to build link, because this is the user's email verification link.

if I write

echo ($ _GET['user_id']);

Then get this:

6? Reg = true

And I try:

echo get_query_var (& # 39; user_id & # 39;);  

But it does not work. What did I do wrong?

I have numerical permalink.