3.5

例子3.1p70

//;使用构造函数修改例子2.3
#include<iostream>
using namespace std;
class Time
{
public:
    Time() {
        hour = 0;
        minute = 0;
        sec = 0;
    }
    void setTime();
    void showTime();
private:
    int hour;
    int minute;
    int sec;
};
void Time::setTime()
{
    cin >> hour >> minute >> sec;
}
void Time::showTime()
{
    cout << hour << ":" << minute << ":" << sec << endl;
}
int main()
{
    Time t1;
    t1.setTime();
    t1.showTime();
    Time t2;
    t2.showTime();
    return 0;
}

例子3.2p72

//两个长方体,已知各自参数,求体积
#include<iostream>
using namespace std;
class Box
{
public:
    Box(int, int, int);
    int volume();
private:
    int height;
    int width;
    int length;
};
Box::Box(int h, int w, int len)
{
    height = h;
    width = w;
    length = len;

}
int Box::volume()
{
    return(height*width*length);
}
int main() {
    Box box(12, 25, 30);
    cout << "The volume of box is " << box.volume() << endl;
    Box box2(15, 30, 21);
    cout << "The volume of box2 is " << box2.volume() << endl;
    return 0;
}

例子3.3p74

//;在例子3.2基础上,构建两个一个无参数,一个有参数
#include<iostream>
using namespace std;
class Box
{
public:
    Box();
    Box(int h, int w, int len) :height(h), width(w), length(len) {}
    int volume();
private:
    int height;
    int width;
    int length;
};
Box::Box()
{
    height = 10;
    width = 10;
    length = 10;
}
int Box::volume()
{
    return(height*width*length);

}
int main()
{
    Box box1;
    cout << "The volume of box1 is " << box1.volume() << endl;
    Box box2(15,30,25);
    cout << "The volume of box2 is " << box2.volume() << endl;
    return 0;
}

例子3.4p

//在例子3.3基础上,构造函数改用含默认参数的,且全为10
#include<iostream>
using namespace std;
class Box
{
public:
    Box(int h = 10, int w = 10, int len = 10);
    int volume();
private:
    int height;
    int width;
    int length;
};
Box::Box(int h, int w, int len)
{
    height = h;
    width = w;
    length = len;
}
int Box::volume()
{
    return (height*width*length);
}
int main()
{
    Box box1;
    cout << "The volume of box1 is " << box1.volume() << endl;
    Box box2(15);
    cout << "The volume of box2 is " << box2.volume() << endl;
    Box box3(15, 30);
    cout << "The volume of box3 is " << box3.volume() << endl;
    Box box4(15, 30, 20);
    cout << "The volume of box4 is " << box4.volume() << endl;

    return 0;
}

例子3.5p79

//;包含析构函数和构造函数//有问题
#include<string>
#include<iostream>
using namespace std;
class Student
{
public:
    Student(int n, string nam, char s)
    {
        num = n;
        name = nam;
        sex = s;
        cout << "Constructor called" << endl;
    }
    ~Student()
    {
        cout << "Destructor called" << endl;
    }
    void display()
    {
        cout << "num:" << num << endl;
        cout << "name:" << name << endl;
        cout << "sex:" << sex << endl << endl;
    }
private:
    int num;
    string name[20];
    char sex;
};
int main()
{
    Student stu1(10010, "Wang_li", 'f');
    stu1.display();
    Student stu2(10011, "Zhang_fan", 'm');
    stu2.display();
    return 0;
}

例子3.6p

//对象数组:计算和输出3个立方体的体积//书上的错误的修改过来了
#include<iostream>
using namespace std;
class Box
{
public:
    Box(int h = 10, int w = 12, int len = 15) :height(h), width(w), length(len) {}
    int volume();
private :
    int height;
    int width;
    int length;
};
int Box::volume()
{
    return (height*width*length);
}
int main()
{
    Box a[3] = {
        Box(10,12,15),
        Box(15,18,20),
        Box(16,20,26)
        //return 0;
    };
    cout << "volume of a[0] is " << a[0].volume() << endl;
    cout << "volume of a[1] is " << a[1].volume() << endl;
    cout << "volume of a[2] is " << a[2].volume() << endl;

}

例子3.7p87

这里很重要,要细心理解

//适用对象指针输出时分秒//这里很重要,要细心理解
#include<iostream>
using namespace std;
class Time
{
public:
    Time(int, int, int);
    int hour;
    int minute;
    int sec;
    void getTime();
private:

};
Time::Time(int h, int m, int s)
{
    hour = h;
    minute = m;
    sec = s;
}
void Time::getTime() {
    cout << hour << ":" << minute << ":" << sec << endl;
}
int main()
{
    Time t1(10, 13, 56);
    int *p1 = &t1.hour;//为何这里有&
    cout << *p1 << endl;

    t1.getTime();
    Time *p2 = &t1;
    p2->getTime();

    void(Time:: *p3)();
    p3 = &Time::getTime;//为什么加了()之后就报错呢
    (t1.*p3)();

    return 0;

}

例子3.8p97

//使用对象的引用,输出时分秒//可以通过类外函数(参数必须为引用,否则无效),修改相关参数
#include<iostream>
using namespace std;
class Time {
public:
    Time(int, int, int);
    int hour;
    int minute;
    int sec;
};
Time::Time(int h, int m, int s)
{
    hour = h;
    minute = m;
    sec = s;
}
void fun(Time &t)//&必须要有,否则无效
{
    t.hour = 18;
    //t.minute = 30;
}
int main()
{
    Time t1(10, 13, 56);//此时里面参数10,已经被该对象的引用给覆盖了
    fun(t1);
    cout << t1.hour<<":"<<t1.minute<<":"<<t1.sec << endl;
    return 0;
}

例子3.9p100

//对象赋值给另外个对象(必须同个类才行)
#include<iostream>
using namespace std;
class Box
{
public:
    Box(int = 10, int = 10, int = 10);//这里居然不用写出变量名
    int volume();
private:
    int height;
    int width;
    int length;
};
Box::Box(int h, int w, int len)
{
    height = h;
    width = w;
    length = len;
}
int Box::volume()
{
    return (height*width*length);
}
int main()
{
    Box box1(15, 30, 25), box2;//即使没有括号()里面,也能运行
    cout << "The volume of box1 is " << box1.volume() << endl;
    box2 = box1;
    cout << "The volume of box2 is " << box2.volume() << endl;
}

例子3.10p105

//使用静态数据成员输出立方体的体积
#include<iostream>
using namespace std;
class Box
{
public:
    Box(int, int);
    int volume();
    static int height;
    int width;
    int length;
};
Box::Box(int w, int len)
{
    width = w;
    length = len;
}
int Box::volume()
{
    return (height*width*length);
}
int Box::height = 10;
int main()
{
    Box box1(15, 20), box2(20, 30);
    cout << box1.height << endl;
    cout << box2.height << endl;
    cout << Box::height << endl;
    cout << box1.volume()<< endl;
    return 0;
}

例子3.11p107

//使用静态成员函数统计学生平均成绩//没有通过编译
#include<iostream>
using namespace std;
class Student
{
public:
    Student(int n,int a,float s):num(n),age(a),score(s){}
    void total();
    static float average();
private:
    int num;
    int age;
    float score;
    static float sum;
    static int count;
};
void Student::total()
{
    sum += score;
    count++;
}
float Student::average()
{
    return(sum / count);
}
int main()
{
    Student stu[3] =
    {
        Student(1001,18,70),
        Student(1002,18,78),
        Student(1005,20,98)
    };//这里必须添加;因为这是数组
    int n;
    cout << "please input the number of students: ";
    cin >> n;
    for (int i = 0; i < n; i++)
        stu[i].total();
    cout<< "the average score of " << n << "students is " << Student::average() << endl;
    return 0;
}

例子3.12p10