多态性问题：关于抽象类与派生类

1.抽象类与派生类的应用（计算图形面积周长）
2.使用对象指针数组完成（各种图形面积实现）

1. 多态性：抽象类和派生类

(1) 定义一个抽象类CShape (至少有一个函数被声明为纯虚函数)；

(2) 再利用CShape分别定义两个派生类CRectangle（矩形）和CCirle（圆）， 三个类都有计算面积的成员函数GetArea()和计算对象周长的成员函数GetPerimeter() ；

(3) 在主函数中声明基类指针和派生类对象，并通过基类指针调用不同对象的成员函数GetArea() 和GetPerimeter()。

直接上代码：

#include<iostream>
#define Pi 3.14159
using namespace std;
class CShape{
protected:
 double x,y;
public:
 void set(double i,double j)
 {
  x=i;
  y=j;
 }
 virtual double GetArea()=0;
 virtual double GetPerimeter()=0;
};
class CRectangle:public CShape{
public:
 double GetArea(){
  return x*y; 
 }
 double GetPerimeter(){
  return 2*x*y;
 }
};
class CCircle: public CShape
{ 
 private:
  double radius;
 public:
  CCircle(double r):radius(r){ }
        double GetArea() { return Pi*radius*radius;}  
        double GetPerimeter() { return 2*Pi*radius; }
};
int main()
{
 CShape *c;
 CCircle i(6.6);
 CRectangle re;
 c=&re;
 c->set(6,6);
 cout<<"CRectangle area:"<<c->GetArea()<<endl;
 cout<<"CRectangle perimeter:"<<c->GetPerimeter()<<endl;
 c=&i;
 cout<<"CCircle area:"<<c->GetArea()<<endl;
 cout<<"CCircle perimeter:"<<c->GetPerimeter()<<endl;
 return 0;
}

 

2．对象指针数组

1. 在第1题基础上再定义三个CShap的派生类CSquare(正方形)、CTrapezoid(梯形)、CTriangle(三角形)；
2. 分别用虚函数计算五种图形的面积，并求它们的和；

要求用基类指针数组，使它的每一个元素指向一个派生类。

代码如下：

#include<iostream>
#define Pi 3.14159
using namespace std;
class CShape{
protected:
 double x,y;
public:
 void set(double i,double j)
 {
  x=i;
  y=j;
 }
 virtual double GetArea()=0;
};

class CRectangle:public CShape{
public:
 double GetArea(){
  return x*y; 
 }
};

class CCircle: public CShape
{ 
 private:
  double radius;
 public:
  CCircle(double r):radius(r){ }
        double GetArea() { return Pi*radius*radius;}  
};

class CSquare: public CShape{
private:
 double side;
public:
 CSquare(double s):side(s){ }
  double GetArea(){ return side*side;}
};

class CTrapezoid:public CShape{
private:
 double high,bottom,waist;
public:
 CTrapezoid(double h,double b,double w):high(h),bottom(b),waist(w){ };
  double GetArea(){ return 0.5*(high+bottom)*waist;}
};

class CTriangle:public CShape{
private:
 double length,width;
public:
 CTriangle(double le,double wi):length(le),width(wi){ };
  double GetArea(){ return 0.5*length*width;}
};
int main()
{
 double sum=0;
 CShape *c;
 CCircle i(6.6);
 CRectangle r;
 CSquare s(8);
 CTrapezoid z(1,2,3);
 CTriangle g(3,4);
 c=&r;
 c->set(6,6);
 sum += c->GetArea();
 cout<<"CRectangle area:"<<c->GetArea()<<endl;
 c=&i;
 sum += c->GetArea();
 cout<<"CCircle area:"<<c->GetArea()<<endl;
 c=&s;
 sum += c->GetArea();
 cout<<"CSquare area:"<<c->GetArea()<<endl;
 c=&z;
 sum += c->GetArea();
 cout<<"CTrapezoid area:"<<c->GetArea()<<endl;
 c=&g;
 sum += c->GetArea();
 cout<<"CTriangle area:"<<c->GetArea()<<endl;
 cout<<"Total area:"<<sum<<endl;
 return 0;
}