C++编程练习：多态实验——设计一个基类Shapes，Shapes类公有派生产生矩形类Rectangle和圆类Circle

//头文件
#include <iostream>
#define PI 3.141265
using namespace std;
class Shapes
{
public:
  virtual void display() = 0;  //成员函数dispaly（）声明为纯虚函数
};
class Rectangle : virtual public Shapes
{
protected:
  float x, y;
public:
  float length;
  float width;
  Rectangle()
  {
  }
  Rectangle(float a, float b)
  {
  x = a;
  y = b;
  }
  virtual float getRectangle()
  {
  return (x * y);
  }
  virtual void display()
  {
  cout << "矩形的长为：" << x << endl;
  cout << "矩形的宽为：" << y << endl;
  cout << "矩形的面积为：" << getRectangle() << endl;
  }
};
class Circle : virtual public Shapes
{
protected:
  int r;
public:
  Circle()
  {
  }
  Circle(float R)
  {
  r = R;
  }
  virtual float getCircle()
  {
  return PI * r * r;
  }
  virtual void display()
  {
  cout << "圆的半径为：" << r << endl;
  cout << "圆的面积为：" << getCircle() << endl;
  }
};

//主函数
#include <iostream>
#include "头文件.h"
#define PI 3.141265
using namespace std;
int main()
{
  Shapes* p;
  double a = 0, b = 0, r = 0;
  cout << "请分别输入矩形的长和宽：" << endl;
  cin >> a >> b;
  Rectangle A(a, b);
  p = &A;
  p->display();
  cout << "" << endl;
  cout << "请输入圆的半径：" << endl;
  cin >> r;
  Circle B(r);
  p = &B;
  p->display();
  system("pause");
  return 0;
}