Function surfaceArea

Examples/Modules/Chapter 12/Ex12_12/Ex12_12.cpp:23–27

friend function to calculate the surface area of a Box object

// friend function to calculate the surface area of a Box object
double surfaceArea(const Box& box)
{
  return 2.0 * (box.m_length * box.m_width
    + box.m_length * box.m_height + box.m_height * box.m_width);
}