Madrid,
I would recommend that you stir away from CINs. If you can compile your C++ code into a DLL, then you can easily call it from LabVIEW. CINs have the disadvantage that if you change your code in anyway, you have to update the CIN node in the diagram of the VI. However if you recompile your DLL, you don't have to inform LabVIEW that you have a newer version of your DLL. If the newer DLL is in the same path that LabVIEW is searching, then it'll link to it automatically.
ActiveX is also a good choice. It might take more development time than creating a DLL though.
My two cents,
Azucena