#include<iostream.h>
#include<math.h>
using namespace std;
class Shape
{
public:
virtual float area() const{return 0.0;}//虚函数
virtual float volume() const{return 0.0;}//虚函数
virtual void shapeName() const=0;//纯虚函数
};
class Point:public Shape
{
public:
Point(float=0,float=0);
void setPoint(float,float);
float getX() const{return x;}
float getY() const{return y;}
virtual void shapeName() const{cout<<"Point: ";}
friend ostream &operator<<(ostream &,const Point &);
protected:
float x,y;
};

Point::Point(float a,float b)
{x=a;y=b;}

void Point::setPoint(float a,float b)
{x=a;y=b;}

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

class Circle:public Point
{
public:
Circle(float x=0,float y=0,float r=0);
void setRadius(float);
float getRadius() const;
virtual float area() const;
virtual void shapeName() const{cout<<"Circle: ";}
friend ostream &operator<<(ostream &,const Circle &);
protected:
float radius;
};

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

void Circle::setRadius(float r):radius(r){}

float Circle::getRadius() const{return radius;}

float Circle::area() const{return 3.14*pow(radius,2);}

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

class Cylinder:public Circle
{
public:
Cylinder(float x=0,float y=0,float r=0,float h=0);
void setHeight(float);
virtual float area() const;
virtual float volume() const;
virtual void shapeName() const{cout<<"Cylinder: ";}
friend ostream &operator<<(ostream &,const Cylinder &);
protected:
float height;
};

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

void Cylinder::setHeight(float h){height=h;}

float Cylinder::area() const
{
return 2*Circle::area()+2*3.14*radius*height;
}

float Cylinder::volume() const
{
return Circle::area()*height;
}

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

int main()
{
Point point(3.2,4.5);
Circle circle(2.4,1.2,5.6);
Cylinder cylinder(3.5,6.4,5.2,10.5);
point.shapeName();
cout<<point<<endl;

circle.shapeName();
cout<<circle<<endl;

cylinder.shapeName();
cout<<cylinder<<endl<<endl;

Shape *pt;

pt=&point;
pt->shapeName();//动态关联
cout<<"x="<<point.getX()<<",y="<<point.getY()<<"\narea="<<pt->area()
<<"\nvolume="<<pt->volume()<<"\n\n";

pt=&circle;
pt->shapeName();
cout<<"x="<<circle.getX()<<",y="<<circle.getY()<<"\narea="<<pt->area()
<<"\nvolume="<<pt->volume()<<"\n\n";

pt=&cylinder;
pt->shapeName();
cout<<"x="<<cylinder.getX()<<",y="<<cylinder.getY()<<"\narea="<<pt->area()
<<"\nvolume="<<pt->volume()<<"\n\n";

return 0;
}


错误显示为:
item.cpp: In member function `void Circle::setRadius(float)':
item.cpp:51: error: only constructors take base initializers