寒假作业2月6号

第五章静态成员与友元

一、填空题

1、一个类的头文件如下所示，num初始化值为5，程序产生对象T，且修改num为10，并使用show()函数输出num的值10。

#include <iostream.h>

class Test

{ private:

static int num;

public:

Test(int);

void show();

};

int test::num = 5;_____

Test::Test(int n)

{ num=n; }

void Test::show()

{ cout<<num<<endl; }

void main()

{ Test t(10);

**** t.show(); __ _____

}

2 、在下面程序的底画线处填上适当的字句，使该程序执行结果为40。

#include <iostream>

class Test

{ public:

__static int x;

Test (int i=0)

{x=i+x;}

int Getnum()

{return Test::x+7;}

};

Int test::x=33_______;

void main()

{Test test;

cout<<test.Getnum()<<endl;

}

3 、下列程序运行的结果是___________

#include <iostream.h>

#include <string.h>

#include <iomanip.h>

class student

{char name［8］;

int deg;

char level［7］;

friend class process; // 说明友元类

public:

student(char na［］,int d)

{ strcpy(name,na);

deg=d;

}

};

class process

{ public:

void trans(student &s)

{int i=s.deg/10;

switch(i)

{case 9:

strcpy(s.level, "优");break;

case 8:

strcpy(s.level,"良");break;

case 7:

strcpy(s.level,"中");break;

case 6:

strcpy(s.level,"及格");break;

default:

strcpy(s.level,"不及格");

}

void show(student &s)

{cout<<setw(10)<<s.name<<setw(4)<<s.deg<<setw(8)<<s.level<<endl;}

};

void main()

{ student st［］={student("张三",78),student("李四",92),student("王五

",62),student("孙六",88)};

process p;

cout<<"结果:"<<"姓名"<<setw(6)<<"成绩"<<setw(8)<<"等级"<<endl;

for(int i=0;i<4;i++)

{ p.trans(st［i］);

p.show(st［i］);}

}

姓名成绩等级

张三 78 中

李四 92 优

王五 62 及格

孙六 88 良

二、编程题

(1) 编写一个类，声明一个数据成员和一个静态数据成员。让构造函数初始化数据成员，并把静态数据成员加1，让析构函数把静态数据成员减1。

(2) 根据(1)编写一个应用程序，创建三个对象，然后显示它们的数据成员和静态数据成员，再析构每个对象，并显示它们对静态数据成员的影响。

(3) 修改(2)，让静态成员函数访问静态数据成员，并让静态数据成员是保户的。

cpp 复制代码

#include <iostream>

using namespace std;

class AAA
{
    friend int static_re();
private:
    int a;
protected:
    static int b;
public:
    AAA(int a):a(a)
    {
        b++;
    }
    ~AAA()
    {
        b--;
        cout << "b=" << b << endl;
    }
    int get_int()
    {
        return a;
    }
    static int get_static()
    {
        return b;
    }
};

int static_re()
{
    AAA::b=100;
    cout << "B:" << AAA::b << endl;
    return AAA::b;
}

int AAA::b=0;

int main()
{
    AAA a1(10),a2(20),a3(30);
    cout << "a1_int=" << a1.get_int() << endl;
    cout << "a2_int=" << a2.get_int() << endl;
    cout << "a3_int=" << a3.get_int() << endl;
    cout << "static=" << a1.get_static() << endl;
    static_re();

    return 0;
}

(1) 下述代码有何错误，改正它。

|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| #include < iostream> using namespace std; class Animal; void SetValue(Animal&, int); void SetValue(Animal&, int, int); class Animal { public: friend void SetValue(Animal&, int); protected: int itsWeight; int itsAge; }; void SetValue(Animal& ta, int tw) { a.itsWeight = tw; ---》ta.itsWeight=tw; } void SetValue(Animal& ta, int tw, int tn) { ta.itsWeight = tw; ta.itsAge = tn; } int main() { Animal peppy; SetValue(peppy, 5); SetValue(peppy, 7,9); return 0; } |

(2) 将上面程序中的友员改成普通函数，为此增加访问类中保护数据的成员函数。

cpp 复制代码

#include <iostream>

class Animal {
public:

    void SetValue(int);

    void SetValue(int, int);

protected:

    int itsWeight;

    int itsAge;

};

void Animal::SetValue(int tw) {
    itsWeight = tw;

}

void Animal::SetValue(int tw, int tn) {
    itsWeight = tw;

    itsAge = tn;

}

int main() {
    Animal peppy;

    peppy.SetValue(5);

    peppy.SetValue(7, 9);

    return 0;

}

重新编写下述程序，使函数Leisure()成为类Car和类Boat的函数。作为重新编程，在类Car和类Boat中，增加函数set()。

|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| #include < iostream> using namespace std; class Boat; class Car { public: Car(int j){size = j;} friend int Leisure(int time, Car& aobj, Boat& bobi); protected: int size; class Boat { public: Boat(int j){size = j;} friend int Leisure(int time, Car& aobj, Boat& bobj); protected: int size; }; int Leisure(int time, Car& aobj, Boat& bobi) { return time * aobj.size *bobi.size; } ｝; int main() { Car c1(2); Boat bl(3); int time = 4; cout << Leisure(time, cl,bl); return 0; } |

cpp 复制代码

 #include <iostream>
using namespace std;

class Boat;

class Car {
public:
    Car(int j) { size = j; }
    int Leisure(int time, Boat& bobj);

    void set(int j) { size = j; }

private:
    int size;
};

class Boat {
public:
    Boat(int j) { size = j; }
    int Leisure(int time, Car& aobj);

    void set(int j) { size = j; }

private:
    int size;
};

int Car::Leisure(int time, Boat& bobj) {
    return time * size * bobj.size;
}

int Boat::Leisure(int time, Car& aobj) {
    return time * size * aobj.size;
}

int main() {
    Car c1(2);
    Boat bl(3);
    int time = 4;

    cout << c1.Leisure(time, bl) << endl;

    return 0;
}