改错题

 #include <iostream.h>

class shape

{public:

virtual int area(){return 0;}

};

class rectangle:public shape

{public:

int a, b;

void setLength (int x, int y) {a=x;b=y;}

int area() {return a*b;}

};

void main()

{rectangle r;

r.setLength(3,5);

shape s1,*s2=&r;

cout <<r.area() <<endl;

s2=s1;

cout <<s2.area()<<endl;

}

答案：shape s1,*s2=r;指针使用错误。s是指针使用它指向对象的成员有两种方法，有下面两行可知，使用的是引用。［修改］改为shape &s=r;