c17_06.cpp

it can help you use C++ program we

// 纯虚函数的使用
#include  <iostream >
using namespace std;

const double PI = 3.14159;

class  CShape //定义一个抽象类
{
public:
	virtual float area() = 0;		//声明为纯虚函数
	virtual void print() = 0;		//声明为纯虚函数
};

class  CCircle:  public  CShape
{
public:
	CCircle( float r ): m_rad(r) {}
	float  area() { return PI * m_rad * m_rad; }
	void print()
	{
		cout << " 圆的面积是：" <<area() << endl;
	}
private:
	float	m_rad;		//圆的半径
};

class  CRectangle: public  CShape  
{
public:
	CRectangle( float w, float h ): m_wid(w), m_hig(h) {}  
	float  area() { return m_wid *  m_hig; }
	void print()
	{
		cout << " 矩形的面积是："<< area() << endl;
	} 
private:
	float	m_wid, m_hig;		//矩形的长和宽
};

int main()
{
	CShape *layoutptr[2];					//定义一个基类类型的指针数组
	layoutptr[0] = new CCircle(3);			//可以让基类类型的指针指向派生类对象
	layoutptr[1] = new CRectangle(2,4);	//可以让基类类型的指针指向派生类对象
	for(int i=0;i<2;i++)
	{
		layoutptr[i]->print();
		delete layoutptr[i];			// 释放占用的资源
	}

	return 0;
}