Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Along
HAIR_SCALE_TYPEParameter: Relative
HAIR_SCALE_RELATIVEParameter: Percent
HAIR_SCALE_PERCENTParameter: Absolute
HAIR_SCALE_ABSOLUTE