该程序无法运行，谁能看一下？

#include<iostream>
using namespace std;

class circle
{ private:
    int x;
    int y;
    int r;
  public:
     circle(int e,int f,int g);
     void  circle::setcircle(int e,int f,int g)
        {x=e;y=f;r=g;}
     int Getx(){return x;}
     int Gety(){return y;}
     int Getr(){return r;}
     void showcircle();
};
 void circle::showcircle()
  {
    cout<<"横坐标为"<<Getx()<<"纵坐标为"<<Gety()<<"圆的半径为"<<Getr()<<endl;
  }
  
int main()
{ double pi=3.14,s;
  circle BC(5,6,7);
  s=pi*BC.Getr()*BC.Getr();
  
  BC.showcircle();
  cout<<"面积为"<<s;
  system("pause");
  return 0;  
   
}
错误：
  C:\DOCUME~1\administrator\LOCALS~1\Temp\ccCscaaa.o(.text+0x1f2) In function `main':
    [Linker error] undefined reference to `circle::circle(int, int, int)'
     C:\DOCUME~1\administrator\LOCALS~1\Temp\ccCscaaa.o(.text+0x1f2) ld returned 1 exit status