#include <iostream.h>
#include <math.h>

const double PI = 2.0 * asin(1.0);
// class declaration

class Circle
{
  protected:
    double radius;
  public:
    Circle(double = 1.0);  // constructor
    double calcval();
};

// implementation section for Circle

// constructor
Circle::Circle(double r)
{
  radius = r;
}

// calculate the area of a circle
double Circle::calcval()
{
  return(PI * radius * radius);
}

// class declaration for the derived class
// Cylinder which is derived from Circle
class Cylinder : public Circle
{
  protected:
    double length;  // add one additional data member and
  public:           // two additional function members
    Cylinder(double r = 1.0, double l = 1.0) : Circle(r), length(l) {}
    double calcval();
};

// implementation section for Cylinder

double Cylinder::calcval()   // this calculates a volume
{
  return length * Circle::calcval(); // note the base function call
}

int main()
{
  Circle circle_1, circle_2(2);  // create two Circle objects
  Cylinder cylinder_1(3,4);      // create one Cylinder object

  cout << "The area of circle_1 is " << circle_1.calcval() << endl;
  cout << "The area of circle_2 is " << circle_2.calcval() << endl;
  cout << "The volume of cylinder_1 is " << cylinder_1.calcval() << endl;

  circle_1 = cylinder_1;  // assign a cylinder to a Circle

  cout << "\nThe area of circle_1 is now " << circle_1.calcval() << endl;

  return 0;
}