/*
Jui-Chen Ma
PS 7 part 1
*/

double surface ( double x, double y );

class Layers {
  double wi;
  double le;
  double (*func[2])(double, double);
public:
  Layers (double w, double l)
    {
      wi=w; le=l;
	      }
  Layers(double w, double l, double (*top)(double, double), double (*b) (double, double))
    {
      wi=w; le=l; func[0]=top; func[1]=b;
    }
  double vol;
  virtual double height(double x, double y)
    { return (*func[0])(x, y) - (*func[1])(x, y); }
  void volume(void);
};