*.WDL files are C-Script files.
*.C files (and lesser *.H files) are Lite-C files.
This extension is the only way the the compiler knows which is which.

C-Script is the older and (in some peoples eyes) weaker language.
It just contains the scripts you write, or that are inserted by the templates.

Lite-C in the newer generation revision, which is much more like real C,C++.
Lite-C ALWAYS has one of these lines at the very top of the "main" file.
#include <acknex.h> or #include <litec.h>.
If you see a line that starts with #include then you know its a Lite-C script.

Other than these differences, Lite-C and C-Script look VERY similar to the untrained eye,
because Lite-C developed from C-Script, and because they still share almost all
the same function/command names.

Best of luck telling them apart......