友元类

问题及描述；

/*
 *Copyright (c) 2016,烟台大学计算机学院
 *All rights reserved.
*文件名称；test.cpp
 *作者；邱凯
 *完成日期；2016年4月17号
 *版本号；v6.0
 *问题描述;  友元类
 *输入描述；  无
 *输出描述； 输出答案
*/
#include <iostream>
using namespace std;
class Date;
class Time
{
public:
    Time(int,int,int);
    void add_a_second(Date &);
    void display(Date &);
private:
    int hour;
    int minute;
    int sec;
};

class Date
{
public:
    Date(int,int,int);
    friend class Time;
private:
   int month;
    int day;
   int year;
};

int main( )
{
    Time t1(23,59,32);
    Date d1(2,28,2013);
   for(int i=0; i<=31; i++)
    {
        t1.add_a_second(d1);
        t1.display(d1);
    }
    return 0;
}

Time::Time(int h,int m,int s)
{
    hour=h;
    minute=m;
    sec=s;
}
Date::Date(int m,int d,int y)
{
    month=m;
    day=d;
    year=y;
}
int days(int m, int y);
void Time::add_a_second(Date &d)
{
    if(++sec>=60) ++minute,sec-=60;
    if(minute>=60) ++hour,minute-=60;
    if(hour>=24) ++d.day,hour-=24;
   if(d.day>days(d.month,d.year)) ++d.month,d.day=1;
    if(d.month>12) ++d.year,d.month-=12;
}
void Time::display(Date &d)
{
   cout<<d.year<<"年"<<d.month<<"月"<<d.day<<"日";
    cout<<hour<<":"<<minute<<":"<<sec<<endl;
}

int days(int m, int y)
{


    int d[]={0,31,28,31,30,31,30,31,31,30,31,30,31};
   if((y%4==0&&y%100!=0)||(y%400==0)) d[2]=29;
    return d[m];
}