Theres a difference between C2 and C3...
C2 is used for stack cleanup for the stdcall/thiscall/fastcall calling conventions because its not done by the caller but by the callee. Depending on the return size it could end up on the stack if its > 4 byte because EAX is 4 byte and cant hold a complete structure which is bigger.
And it would be nice if you could stop acting like you know anything and I nothing. You have actually no Idea what I know and what not so please dont post those comments since you actually write the same with just some more words.

And in short: C3 is the command for "RETN" in assembler written in hex.
You dont have to learn any assembler to code with 3dgs, was just saying that void actually changes the compiler behaviour together with the calling convention.