Question about HL

I'm taking programming at my school, learned C++ last year, and im learning Java this year, so I was wondering, what language is HL written in?

If it's something I know, I might want to take a look inside the box so to speak.

Half-Life was written in C++.
You'll find some core engine code is in C, since it's more or less taken from Quake 1, but it's only really a matter of style change.
You can get the SDK here.

Cool thanks, I'll take a look.