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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.
(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。
#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;
}
2.
(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。
#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;}
3. 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; } |
#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;
}