磁县二手车:我想问一下这道C＋＋的程序在哪出错

#include<iostream.h>

class Shape
{public:
Shape(double=0.0,double=0.0);
virtual void setpoint()=0;
protected:
double x,y;
};
Shape::Shape(double a,double b)
{x=a;
y=b;}

class TwoDimShape:public Shape
{public:
TwoDimShape(double=0.0,double=0.0);
void setpoint()
{cout<<"the point of the center is : "<<'('<<x<<","<<y<<')'<<endl;}
virtual void setSide(){}
};
TwoDimShape::TwoDimShape(double a,double b):Shape(a,b){}

class Circle:public TwoDimShape
{public:
Circle(double=0,double=0.0,double=0.0);
void setSide(double);
void putSide(){cout<<"the Radius of the circle is :"<<Radius<<endl;}
protected:
double Radius;
};
Circle::Circle(double r,double a,double b):TwoDimShape(a,b)
{setSide(r);}
void Circle::setSide(double r)
{Radius=r;
}
void main()
{Circle c(1.5,2.1,1.1);
c.setpoint();
c.putSide();}

问题说明：
virtual void setSide()=0;//改成virtual void setSide(){}