阅读以下说明和C++程序，将应填入(n)处的字句写在对应栏内。

【说明】

以下程序的功能是计算正方体、球体和圆柱体的表面积和体积并输出。

程序由4个类组成：类cube、sphere和cylinder分别表示正方体、球体和圆柱体；抽象类 container为抽象类，提供了两个纯虚拟函数surface_area()和volum()，作为通用接口。

【C++程序】

include＜iostream.h＞

define pi 3.1416

class container｛

protected:

double radius;

public:

container(double radius) {container::radius=radius;}

virtual double surface_area()=0;

virtual double velum()=0;

};

class cube:(1){ //定义正方体类

public:

cube(double radius):container(radius){};

double surface_area () {return 6 * radius * radius;}

double volum() {return radius * radius * radius;}

};

class sphere:(2){ //定义球体类

public:

sphere(double radius): container(radius){};

double surface_area() { return (3);}

double volum() {return pi * radius * radius * radius * 4/3;}

};

class cylinder:(4){ //定义圆柱体类

double height;

public:

cylinder(double radius,double height):container(radius)

{

container::height=height;

}

double surface_are a () { return 2 * pi * radius * (height+radius); }

double volum () {return (5);}

};

void main()

{

container * p;

cube obj1 (5);

sphere obj2(5);

cylinder obj3(5,5);

p=&obj1;

cout＜＜“正方体表面积”(＜＜p-＞surface_area()＜＜end1;

cont＜＜“正方体体积”＜＜p-＞volume()＜＜end1;

p=&obj2;

cout＜＜“球体表面积”＜＜p-＞surface_area()＜＜end1;

cout＜＜“球体体积”＜＜p-＞volume()＜＜end1;

p=&obj3;

cout＜＜“球体表面积”＜＜p-＞surface_area()＜＜end1;

cout＜＜“球体体积”＜＜p-＞volume()＜＜end1;

}