#include <iostream>

using namespace std;

 

const float PI = (float)3.14159;

 

class Shape{

public:

    virtual float CalCircumference()=0;

    virtual float CalArea()=0;

};

 

//圆形

class Roundness: public Shape{

public:

    Roundness(float r):radius(r)

    {}

     

    virtual float CalCircumference()

    {

        return 2 * PI * radius;

    }

     

    virtual float CalArea()

    {

        return PI * radius * radius;

    }

private:

    float radius;

};

 

//正方形

class Square: public Shape{

public:

    Square(float w):width(w)

    {}

     

    virtual float CalCircumference()

    {

        return 4 * width;

    }

     

    virtual float CalArea()

    {

        return width * width;

    }

private:

    float width;

};

 

//长方形

class Rectangle: public Shape{

public:

    Rectangle(float w, float h):width(w), hight(h)

    {}

     

    virtual float CalCircumference()

    {

        return 2 * (width + hight);

    }

     

    virtual float CalArea()

    {

        return hight * width;

    }

private:

    float width;

    float hight;

};

 

void main()

{

    Shape* roud = new Roundness(3);

    Shape* squ = new Square(3);

    Shape* rang = new Rectangle(3, 4);

 

    cout<<"圆形的周长:"<<roud->CalCircumference()<<" 面积："<<roud->CalArea()<<endl;

    cout<<"正方形的周长:"<<squ->CalCircumference()<<" 面积："<<squ->CalArea()<<endl;

    cout<<"长方形的周长:"<<rang->CalCircumference()<<" 面积："<<rang->CalArea()<<endl;

 

}

定义一个公共基类Shape，它表示一个封闭平面几何图形。

然后，从Shape类派生出三角形类Triangle、矩形类Rectangle和圆类Circle，

在基类中定义纯虚函数show和area，分别用于显示图形信息和求相应图形的面积，

并在派生类中根据不同的图形实现相应的函数。要求实现运行时的多态性。

#include <cmath>

#include<iostream>

using namespace std;

const double PI = 3.1415926535;

class Shape

{ public:
virtual  void show( ) = 0;
virtual  double area( ) = 0;

 };

class Rectangle: public Shape

{public:

Rectangle( ){length = 0; width = 0; } 

Rectangle(double len, double wid){ length = len; width = wid; }

double area( ){return length*width;} 

void show( )

{ cout << "length = " << length << '\t' << "width = " << width << endl; } 

private:

double length, width; 

};

class Triangle: public Shape

{public:
Triangle( ){a = 0; b = 0; c = 0;}
Triangle(double x, double y, double z){a = x; b = y; c = z;}
double area( )

{  double s = (a+b+c)/2.0;

   return sqrt(s*(s - a)*(s - b)*(s - c));

} 
void show( )

{cout << "a = " << a << '\t' << "b = " << b << '\t' << "c = " << c << endl;}

private:

double a, b, c; 

};

class Circle: public Shape

{public:

Circle( ){radius = 0; }

Circle(double r){radius = r;}

double area( ){return PI*radius*radius;} 

void show( ){cout << "radius =" << radius << endl;}

private:

double radius;

};

int main( )

{    Shape *s = NULL;
Circle c(10);
Rectangle r(6, 8);
Triangle t(3, 4, 5);
c. show( );
cout << "圆面积：" << c.area( ) << endl;
s = &r;
s -> show( );
cout << "矩形面积：" << s -> area( ) << endl;
s = &t;
s -> show( );
cout << "三角形面积：" << s -> area( ) << endl;
return 0;

}

C+编程：编写一个程序,定义抽象基类Shape，由它派生出5个派生类：Cricle(圆形),Square(正方形)， Rectangle(矩形)， Trapezoid (梯形),Triangle(三角形)。用虚函数分别计算图形面积，并求所有图形面积的和．要求用基类指针数组，使它的每一个元素指向一个派生类对象。
以下是此题的【c++源代码】
#include 
using namespace std;
//定义抽象基类Shape
class Shape
{public:
virtual double area() const =0;                                //纯虚函数
};
//定义Circle(圆形)类
class Circle:public Shape
{public:
Circle(double r):radius(r){}                                     //结构函数
virtual double area() const {return 3.14159*radius*radius;};   //定义虚函数
protected:
double radius;                                                 //半径
};
//定义Square(正方形)类
class Square:public Shape
{public:
Square(double s):side(s){}                                     //结构函数
virtual double area() const {return side*side;}                //定义虚函数
protected:
double side;
};
//定义Rectangle(矩形)类
class Rectangle:public Shape
{public:
Rectangle(double w,double h):width(w),height(h){}               //结构函数
virtual double area() const {return width*height;}              //定义虚函数
protected:
double width,height;                                           //宽与高
};
//定义Trapezoid(梯形)类
class Trapezoid:public Shape
{public:
Trapezoid(double t,double b,double h):top(t),bottom(t),height(h){} //结构函数
virtual double area() const {return 0.5*(top+bottom)*height;}      //定义虚函数
protected:
double top,bottom,height;                                          //上底、下底与高
};
//定义Triangle(三角形)类
class Triangle:public Shape
{public:
Triangle(double w,double h):width(w),height(h){}                //结构函数
virtual double area() const {return 0.5*width*height;}          //定义虚函数
protected:
double width,height;                                            //宽与高
};
int main()
{
Circle circle(12.6);                                             //建立Circle类对象circle
Square square(3.5);                                              //建立Square类对象square
Rectangle rectangle(4.5,8.4);                                    //建立Rectangle类对象rectangle
Trapezoid trapezoid(2.0,4.5,3.2);                                //建立Trapezoid类对象trapezoid
Triangle triangle(4.5,8.4);                                      //建立Triangle类对象
Shape *pt[5]={&circle,&square,&rectangle,&trapezoid,&triangle};
//定义基类指针数组pt，使它每一个元素指向一个派生类对象
double areas=0.0;                                                //areas为总面积
for(int i=0;i<5;i++)
{areas=areas+pt[i]->area();}
cout<
return 0;
}

编写一个程序，声明抽象基类Shape，由它派生出3个派生类：Circle(圆形)、Rectangle(矩形)、Triangle(三角形)，用一个函数pritArea分别输出以上三者的面积，3个图形的数据在定义对象时给定。
以下是此题的【c++源代码】
#include 
using namespace std;
//定义抽象基类Shape
class Shape
{public:
virtual double area() const =0;            //纯虚函数
};
//定义Circle类
class Circle:public Shape
{public:
Circle(double r):radius(r){}                                     //结构函数
virtual double area() const {return 3.14159*radius*radius;};   //定义虚函数
protected:
double radius;                                                 //半径
};
//定义Rectangle类
class Rectangle:public Shape
{public:
Rectangle(double w,double h):width(w),height(h){}               //结构函数
virtual double area() const {return width*height;}              //定义虚函数
protected:
double width,height;                                           //宽与高
};
class Triangle:public Shape
{public:
Triangle(double w,double h):width(w),height(h){}                //结构函数
virtual double area() const {return 0.5*width*height;}          //定义虚函数
protected:
double width,height;                                            //宽与高
};
//输出面积的函数
void printArea(const Shape &s)
{cout<
int main()
{
Circle circle(12.6);                                             //建立Circle类对象circle
cout<
printArea(circle);                                               //输出circle的面积
Rectangle rectangle(4.5,8.4);                                    //建立Rectangle类对象rectangle
cout<
printArea(rectangle);                                            //输出rectangle的面积
Triangle triangle(4.5,8.4);                                      //建立Triangle类对象
cout<
printArea(triangle);           //输出triangle的面积
return 0;
}