OJ输出日期时间——友元函数

#include <iostream>
#include <iomanip>
using namespace std;
class Time;
class Date
{
public:
Date(){}
Date(int y,int mo,int d):year(y),month(mo),day(d){}
friend void display(const Date &,const 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){}
friend void display(const Date &,const Time &);
private:
int hour;
int minute;
int second;
};
void display(const Date &d1,const Time &t1)
{
cout<<d1.year<<"/"<<d1.month<<"/"<<d1.day<<endl;
cout<<t1.hour<<":"<<t1.minute<<":"<<t1.second<<endl;
}
int main()

{

void display(const Date &,const Time &);

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);

display(d1,t1);

return 0;

}