Method volume

Examples/NoModules/Chapter 15/Ex15_11/Box.h:11–11

  Box(double l, double w, double h) : m_length {l}, m_width {w}, m_height {h} {}

  double volume() const override { return m_length * m_width * m_height; }

protected:   // Should be private in production-quality code (add getters to access)
  double m_length, m_width, m_height;