Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Radius
HAIR_TOOL_ADDROOT_RADIUS
Parameter: Step
HAIR_TOOL_ADDROOT_STEP
Parameter: Count
HAIR_TOOL_ADDROOT_COUNT
Parameter: Length
HAIR_TOOL_ADDROOT_LENGTH
Parameter: Min Spacing
HAIR_TOOL_ADDROOT_MINSPACING
Parameter: Pressure
HAIR_TOOL_ADDROOT_PEN
Parameter: Interpolated
HAIR_TOOL_ADDROOT_INTERPOLATE
Parameter: Strength
HAIR_TOOL_ADDROOT_INTERPOLATE_STRENGTH