Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Radius
PRIM_CYLINDER_RADIUS
Parameter: Height
PRIM_CYLINDER_HEIGHT
Parameter: Height Segments
PRIM_CYLINDER_HSUB
Parameter: Rotation Segments
PRIM_CYLINDER_SEG
Parameter: Switch to Updated Cylinder
PRIM_CYLINDER_SWITCH_TO_UPDATED
Parameter: Caps
PRIM_CYLINDER_CAPS
Parameter: Cap Segments
PRIM_CYLINDER_CSUB
Parameter: Fillet
PRIM_CYLINDER_FILLET
Parameter: Fillet Segments
PRIM_CYLINDER_FSUB
Parameter: Fillet Radius
PRIM_CYLINDER_FILLETRADIUS