OJ输出日期时间--友元类

#include <iostream>

using namespace std;
class Time;
class Date
{
public:
Date() {}
Date(int y,int mo,int d):year(y),month(mo),day(d) {}
friend class Time;
private:
int year;
int month;
int day;
};
class Time
{
public:
Time() {}
Time(int h,int mi,int s):hour(h),minute(mi),second(s) {}
void display(Date &d)
{
cout<<d.year<<"/"<<d.month<<"/"<<d.day<<endl;
cout<<hour<<":"<<minute<<":"<<second<<endl;
}

private:
int hour;
int minute;
int second;
};
int main()
{
int year,month,day;
cin>>year>>month>>day;
Date d1(year,month,day);
int hour,minute,second;
cin>>hour>>minute>>second;
Time t1(hour,minute,second);
t1.display(d1);
return 0;
}