Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Inner Radius
PRIM_STAR_IRAD
Parameter: Outer Radius
PRIM_STAR_ORAD
Parameter: Twist
PRIM_STAR_TWIST
Parameter: Points
PRIM_STAR_POINTS