1   // Fig. 9.9: circle2.h
2   // Definition of class Circle
3   #ifndef CIRCLE2_H
4   #define CIRCLE2_H
5   
6   #include "point2.h"
7   
8   class Circle : public Point {
9      friend ostream &operator<<( ostream &, const Circle & );
10  public:
11     // default constructor
12     Circle( double r = 0.0, int x = 0, int y = 0 );
13     void setRadius( double );    // set radius
14     double getRadius() const;    // return radius
15     double area() const;         // calculate area
16  protected:          // accessible to derived classes
17     double radius;   // radius of the Circle
18  };
19  
20  #endif
21  
22  
23  // Fig. 9.9: circle2.cpp
24  // Member function definitions for class Circle
25  #include <iostream.h>
26  #include <iomanip.h>
27  #include "circle2.h"
28  
29  // Constructor for Circle calls constructor for Point
30  // with a member initializer and initializes radius
31  Circle::Circle( double r, int a, int b )
32     : Point( a, b )       // call base-class constructor
33  { setRadius( r ); }
34  
35  // Set radius
36  void Circle::setRadius( double r ) 
37     { radius = ( r >= 0 ? r : 0 ); }
38  
39  // Get radius
40  double Circle::getRadius() const { return radius; }
41  
42  
43  // Calculate area of Circle
44  double Circle::area() const
45     { return 3.14159 * radius * radius; }
46  
47  // Output a circle in the form:
48  // Center = [x, y]; Radius = #.##
49  ostream &operator<<( ostream &output, const Circle &c )
50  {
51     output << "Center = " << static_cast< Point > ( c )
52            << "; Radius = " 
53            << setiosflags( ios::fixed | ios::showpoint )
54            << setprecision( 2 ) << c.radius;
55  
56     return output;   //  enables cascaded calls
57  }
58  
59  
60  // Fig. 9.9: fig09_09.cpp
61  // Driver for class Circle
62  #include <iostream.h>
63  #include "point2.h"
64  #include "circle2.h"
65  
66  int main()
67  {
68     Circle c( 2.5, 37, 43 );
69  
70     cout << "X coordinate is " << c.getX()
71          << "\nY coordinate is " << c.getY()
72          << "\nRadius is " << c.getRadius();
73  
74     c.setRadius( 4.25 );
75     c.setPoint( 2, 2 );
76     cout << "\n\nThe new location and radius of c are\n"
77          << c << "\nArea " << c.area() << '\n';
78  
79     Point &pRef = c;
80     cout << "\nCircle printed as a Point is: " << pRef << endl;
81  
82     return 0;
83  }