You´re correct about this: in C-Script you can´t define your own structs or classes, you have to live with the predefined objects (entities, panels, views ...). So you can use the SDK and program in C++, or - if you don´t need classes - you can use Lite-C, Gamestudios new scripting language (it will replace C-Script gradually in the future), which is almost identical to C.
You can use the SDK with the com version.