All development resources can be found in the development blog. Online resources are available as:
C++ and Python examples can also be found on GitHub in the PluginCafé repository. Since the C++ and Python API present the same classes and functions, Python developers can also consult the C++ documentation.
The Registered Developer program allows 3rd-party developers to register at MAXON. With this registration the SDK Team is able to inform you about the latest releases and changes in the Cinema 4D API. For any further detail feel free to visit the MAXON Registered Developer blog entry describing in detail the Registered Developer program.
MAXON's SDK Team