已定义一个Shape抽象类，在此基础上派生出矩形Rectangle和圆形Circle类，二者都有GetPerim（）函数计算对象的周长，并编写测试main（）函数。

class Shape

{public:

Shape(){}

~Shape(){}

virtual float GetPerim()=0;

}

答案：class Rectangle:public Shape

{public:

Rectangle(float i,float j):L(i),W(j){}

~Rectangle(){}

float GetPerim(){return 2*(L+W);}

private:

float L,W;

};

class Circle:public Shape

{public:

Circle(float r):R(r){}

float GetPerim(){return 3.14*2*R;}

private:

float R;

};

void main()

{Shape * sp;

sp=new Circle(10);

cout<<sp->GetPerim ()<<endl;

sp=new Rectangle(6,4);

cout<<sp->GetPerim()<<endl;

}