c++中 unresolved external symbol_main 是什么意思? 下面是我的程序.出现这个错误,怎么解决?谢谢!

#include<iostream.h>
class point
{
public:
point(int xx=0,int yy=0) {X=xx;Y=yy;}
point(point &p);
int GetX() { return X ;}
int GetY() { return Y ;}
private:
int X,Y;
};

point::point(point &p)
{
X=p.X;
Y=p.Y;
cout<<"拷贝构造函数被调用"<<endl;
}

void fun1(point p)
{
cout<<p.GetX()<<endl;
}

point fun2()
{
point A(1,2);
return A;
}

int mian()
{
point A(4,5);
point B(A);
cout<<B.GetX()<<endl;
fun1(B);
B=fun2();
cout<<B.GetX()<<endl;
return (1);
}