#include <iostream>
using namespace std;
class Clock
{
public:
    Clock(int hour=0, int minute=0, int second=0):hour(hour), minute(minute), second(second) {}
    //void showTime();
    Clock&  operator++ ();
    Clock operator++ (int);
    friend ostream & operator<< (ostream &out,const Clock &c);
private:
    int hour, minute, second;
};

//void Clock::showTime()
//{
//    cout<<hour<<":"<<minute<<":"<<second<<endl;
//}
ostream & operator<< (ostream &out ,const Clock &c)
{
    out<<c.hour<<":"<<c.minute<<":"<<c.second<<"\n";
    return out;
}
Clock &Clock::operator++()
{
    second++;
    if(second>=60)
    {
        minute++;
        second = second%60;
        if(minute>=60)
        {
            hour = (hour+1)%24;
            minute = minute%60;
        }
    }
    return * this;
}
Clock Clock::operator++(int)
{
    Clock old = * this;
    ++ ( * this);
    return old;
}

int main()
{
    Clock c(23,58,59);
    cout<<c;
    //c.showTime();
    //(c++).showTime();
    //(++c).showTime();
    return 0;
}
程序有错，求大神解