C or C++?

[eerok]

C++ is more needed to do Half-Life 2 (game) modifying (code-wise)

That's a good enough answer to your question: focus on what you're going to use.

I am 15 and would like the easier one.

Well, I'm 51 (I'm expecting wisdom and maturity to overtake me Any Day Now ...)

Anyway, if you spend time and effort on C first, and that's not what you're going to be using, that doesn't seem the easiest way to me.