#include <iostream.h>		#define Pi 3.1415926		class Point {		friend ostream &operator << (ostream &, const Point &);		public:		   Point ( float x = 0, float y = 0 ) : x(x) , y(y) { } ;					//默認的構造函數		   void setPoint ( float, float );					//設置坐標值		   float getX ( ) const { return x; }				//取得x坐標值		   float getY ( ) const { return y; }				//取得y坐標值		protected:								//允許派生類訪問		   float x, y;							//點(類Point的對象)的坐標值		};		class Circle : public Point {					//類Circle繼承了類Point		friend ostream &operator << ( ostream &, const Circle & );		public:		   Circle ( float r = 0.0, float x = 0, float y = 0 ):			radius(r) { center.x = x; center.y = y; }; 		//默認的構造函數		   void setRadius ( float );					//設置半徑值		   float getRadius ( ) const { return 2*radius; }					//取得半徑值		   float area ( ) const { return Pi*Pi*radius; }						//計算圓面積		protected:		   float radius;		   Point center;		} ;		ostream & operator << (ostream& os, const Point & p) {		    os << endl << "the point is located at ( " ;		    os << p.x << "," << p.y << ")" << endl;		    return os;		}		ostream & operator << (ostream& os, const Circle & c) {		    os << "the center of circle is located at ( ";		    os << " )" <<endl;		    os << "the radius is " << c.radius << endl;		    return os;		}		main () {		   Point * pointPtr, p ( 3.5, 5.3 );				//點p坐標為3.5, 5.3		   Circle * circlePtr, c ( 2.7, 1.2, 8.9 );				//圓c半徑為2.7, 坐標為1.2, 8.9		   cout << "Point p: " << p << "\n Circle c: " << c << endl;		   pointPtr = & c;							//把派生類Circle對象的地址賦給了基類指針pointPtr		   circlePtr = ( Circle * ) pointPtr;				//把基類指針強制轉換為派生類指針		   cout << "\n Area of c (via circlePtr) : " << circlePtr -> area ( ) << endl;		   pointPtr = & p;							//把基類Point對象地址賦給基類指針pointPtr		   circlePtr = ( Circle * ) pointPtr;				//把基類指針強制轉換為派生類指針		   cout << "\n Radius of object circlePtr point to : " << circlePtr -> getRadius ( ) << endl;		   return 0;		}