Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Iteration Start
GV_ITERATE_INPUT_LOWERParameter: Iteration End
GV_ITERATE_INPUT_UPPERParameter: On
GV_ITERATE_OPERATOR_ONParameter: Iteration
GV_ITERATE_OUTPUTParameter: Count
GV_ITERATE_OUTPUT_COUNT