项目3

#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;};class Date{public:    Date(int,int,int);    friend class Time; //Time为Date的友元类private:    int month;    int day;    int year;};int main( ){    Time t1(23,59,32);    Date d1(12,25,2012);    for(int i=0; i<=80; i++)    {        t1.add_a_second(d1);        t1.display(d1);    }    return 0;}//下面定义两个类中的成员函数，要求不得再增加成员函数//注意体会在Time的成员函数中可以调用Date类的私有数据成员   Date::Date(int m,int d,int y){    month=m;day=d;    year=y;}Time::Time(int h,int m,int s){    hour=h;    minute=m;    sec=s;}void Time::add_a_second(Date &a){   sec+=1;   if(sec==60){     minute+=1; sec=0; if(minute==60){   hour+=1;   minute=0;   if(hour==24){   a.day+=1;   hour=0;   if(a.day>31){   a.month+=1;   a.day=1;   if(a.month>12){   a.year+=1;   a.month=1;   }   }   }  }        }}void Time::display(Date &a){cout<<a.year<<":"<<a.month<<":"<<a.day<<":"<<hour<<":"<<minute<<":"<<sec<<endl;}