C++程序设计（第三版） 谭浩强 习题9.11 个人设计

习题 9.11 将例9.13中的Time类声明为Date类的友元类，通过Time类中的display函数引用Date类对象的私有数据，输出年、月、日和时、分、秒。

代码块：

#include <iostream>
using namespace std;
class Date;
class Time
{
public:
    Time(int h, int m, int s): hour(h), minute(m), sec(s){};
    void display(Date &);
private:
    int hour;
    int minute;
    int sec;
};
class Date
{
public:
    friend Time;
    Date(int m, int d, int y): month(m), day(d), year(y){};
private:
    int month;
    int day;
    int year;
};
void Time::display(Date &d)
{
    cout<<d.month<<"/"<<d.day<<"/"<<d.year<<endl;
    cout<<hour<<":"<<minute<<":"<<sec<<endl;
}
int main()
{
    Time t1(10, 13, 56);
    Date d1(12, 25, 2004);
    t1.display(d1);
    system("pause");
    return 0;
}