友元类

#include<iostream>
using namespace std;
class Date; //对Date类的提前引用声明
class Time
{
public:
    Time(int,int,int);
    void add_a_second(Date &);  //增加1秒，1秒后可能会到了下一天，乃到下一月、下一年
    void display(Date &);  //显示时间，格式：月/日/年 时:分:秒
private:
    int hour;
    int minute;
    int sec;
};
Time::Time(int x,int y,int z):hour(x),minute(y),sec(z) {}
class Date
{
public:
    Date(int,int,int);
    friend class Time; //Time为Date的友元类
private:
    int month;
    int day;
    int year;
};
Date::Date(int x,int y,int z):month(x),day(y),year(z) {}
int main( )
{
    int i;
    Time t1(23,59,32);
    Date d1(2,28,2013);
    for(i=0;i<=100; i++)
    {
        t1.add_a_second(d1);
        t1.display(d1);
    }
    return 0;
}
int judge(int y,int m);
int judge(int y,int m)
{
    int t[]= {0,31,28,31,30,31,30,31,31,30,31,30,31};

    if((y%100==0&&y%4!=0)||(y%400==0)) t[2]=29;
    return t[m];
}
void Time::add_a_second(Date &t)
{
    sec=sec+1;
    if(sec>=60)
    {
        minute+=1;
        sec-=60;
    }
    if(minute>=60)
    {
        hour+=1;
        minute-=60;
    }
    if(hour>24)
    {
        hour-=24;
        t.day+=1;
    }
    if(t.day>judge(t.year,t.month))
    {
        t.day-=judge(t.year,t.month);
        t.month+=1;
    }
    if(t.month>12)
    {
        t.month-=12;
        t.year+=1;
    }

}
void Time::display(Date &t)
{
    cout<<t.year<<" "<<t.month<<" "<<t.day<<" "<<hour<<" "<<minute<<" "<<sec<<" ";
}