C++语言基础 例程 案例：一个接口，多种方法

贺老师的教学链接  本课讲解

用指针输出几何体

#include <iostream>
using namespace std;

class Point
{
public:
    Point(double x=0,double y=0);
    friend ostream & operator<<(ostream &,const Point &);
protected:
    double x,y;
};

Point::Point(double a,double b):x(a), y(b){}

ostream & operator<<(ostream &output,const Point &p)
{
    output<<"  点：["<<p.x<<","<<p.y<<"]"<<endl;
    return output;
}

class Circle:public Point
{
public:
    Circle(double x=0,double y=0,double r=0);
    double area ( ) const;
    friend ostream &operator<<(ostream &,const Circle &);
protected:
    double radius;
};

Circle::Circle(double a,double b,double r):Point(a,b),radius(r) { }
double Circle::area( ) const
{
    return 3.14159*radius*radius;
}
ostream &operator<<(ostream &output,const Circle &c)
{
    output<<"  圆：Center=["<<c.x<<","<<c.y<<"],r="<<c.radius<<",area="<<c.area( )<<endl;
    return output;
}

class Cylinder:public Circle
{
public:
    Cylinder (double x=0,double y=0,double r=0,double h=0);
    double area( ) const;
    friend ostream& operator<<(ostream&,const Cylinder&);
protected:
    double height;
};

Cylinder::Cylinder(double a,double b,double r,double h):Circle(a,b,r),height(h) {}

double Cylinder::area( ) const
{
    return 2*Circle::area( )+2*3.14159*Circle::radius*height;
}

ostream &operator<<(ostream &output,const Cylinder& cy)
{
    output<<"  圆柱：Center=["<<cy.x<<","<<cy.y<<"],r="<<cy.radius<<",h="<<cy.height
          <<",area="<<cy.area( )<<endl;
    return output;
}

int main( )
{
    Cylinder cy1(3.5, 6.4, 5.2, 10);
    cout<<cy1<<endl;

    Point *p=&cy1;
    cout<<"用指向点的指针输出："<<endl;
    cout<<(*p);

    Circle *c= &cy1;
    cout<<"用指向圆的指针输出："<<endl;
    cout<<(*c);

    Cylinder *cy= &cy1;
    cout<<"用指向圆柱的指针输出："<<endl;
    cout<<(*cy)<<endl;
    return 0;
}

用引用输出几何体

#include <iostream>
using namespace std;

class Point
{
public:
    Point(double x=0,double y=0);
    friend ostream & operator<<(ostream &,const Point &);
protected:
    double x,y;
};

Point::Point(double a,double b):x(a), y(b){}

ostream & operator<<(ostream &output,const Point &p)
{
    output<<"  点：["<<p.x<<","<<p.y<<"]"<<endl;
    return output;
}

class Circle:public Point
{
public:
    Circle(double x=0,double y=0,double r=0);
    double area ( ) const;
    friend ostream &operator<<(ostream &,const Circle &);
protected:
    double radius;
};

Circle::Circle(double a,double b,double r):Point(a,b),radius(r) { }

double Circle::area( ) const
{
    return 3.14159*radius*radius;
}
ostream &operator<<(ostream &output,const Circle &c)
{
    output<<"  圆：Center=["<<c.x<<","<<c.y<<"],r="<<c.radius<<",area="<<c.area( )<<endl;
    return output;
}

class Cylinder:public Circle
{
public:
    Cylinder (double x=0,double y=0,double r=0,double h=0);
    double area( ) const;
    friend ostream& operator<<(ostream&,const Cylinder&);
protected:
    double height;
};

Cylinder::Cylinder(double a,double b,double r,double h):Circle(a,b,r),height(h) {}

double Cylinder::area( ) const
{
    return 2*Circle::area( )+2*3.14159*Circle::radius*height;
}

ostream &operator<<(ostream &output,const Cylinder& cy)
{
    output<<"  圆柱：Center=["<<cy.x<<","<<cy.y<<"],r="<<cy.radius<<",h="<<cy.height
          <<",area="<<cy.area( )<<endl;
    return output;
}

int main( )
{
    Cylinder cy1(3.5, 6.4, 5.2, 10);
    cout<<cy1<<endl;

    cout<<"使用引用："<<endl;
    Point &pRef=cy1;
    cout<<"用点的引用输出："<<endl;
    cout<<pRef<<endl;

    Circle &cRef=cy1;
    cout<<"用圆的引用输出："<<endl;
    cout<<cRef<<endl;

    Cylinder &cyRef=cy1;
    cout<<"用圆柱的引用输出："<<endl;
    cout<<cyRef<<endl;
    return 0;
}

输出几何体面积

#include <iostream>
using namespace std;

class Point
{
public:
    Point(double x=0,double y=0);
    friend ostream & operator<<(ostream &,const Point &);
protected:
    double x,y;
};

Point::Point(double a,double b):x(a), y(b){}

ostream & operator<<(ostream &output,const Point &p)
{
    output<<"  点：["<<p.x<<","<<p.y<<"]"<<endl;
    return output;
}

class Circle:public Point
{
public:
    Circle(double x=0,double y=0,double r=0);
    double area ( ) const;
    friend ostream &operator<<(ostream &,const Circle &);
protected:
    double radius;
};

Circle::Circle(double a,double b,double r):Point(a,b),radius(r) { }

double Circle::area( ) const
{
    return 3.14159*radius*radius;
}

ostream &operator<<(ostream &output,const Circle &c)
{
    output<<"  圆：Center=["<<c.x<<","<<c.y<<"],r="<<c.radius<<",area="<<c.area( )<<endl;
    return output;
}

class Cylinder:public Circle
{
public:
    Cylinder (double x=0,double y=0,double r=0,double h=0);
    double area( ) const;
    friend ostream& operator<<(ostream&,const Cylinder&);
protected:
    double height;
};

Cylinder::Cylinder(double a,double b,double r,double h):Circle(a,b,r),height(h) {}

double Cylinder::area( ) const
{
    return 2*Circle::area( )+2*3.14159*Circle::radius*height;
}

ostream &operator<<(ostream &output,const Cylinder& cy)
{
    output<<"  圆柱：Center=["<<cy.x<<","<<cy.y<<"],r="<<cy.radius<<",h="<<cy.height
          <<",area="<<cy.area( )<<endl;
    return output;
}

int main( )
{
    Cylinder cy1(3.5, 6.4, 5.2, 10);

    Circle *c= &cy1;
    Cylinder *cy= &cy1;

    cout<<"关于面积："<<endl;
    cout<<"用指向圆的指针输出："<<endl;
    cout<<c->area()<<endl;
    cout<<"用指向圆柱的指针输出："<<endl;
    cout<<cy->area()<<endl<<endl;
    return 0;
}