I played a nice game and i wanted to add the guy,but i didnt know how.Later i discovered that you need this code and name.But if you don´t remember the name what do you do?
My suggestion: Add a recently played with ... or last game played with... so you can add your last opponent easily.

Good Idea

Just after a battle, during the victory/defeat screen, you can click their name and then click add as friend.
But other than that, you're screwed if you don't have their number.