C++中++运算符的重载

    void showTime() const;
    Clock& operator ++();
    Clock operator ++(int);
private:
    int hour,minute,second;
};
Clock::Clock(int hour,int minute,int second){
    if(0<=hour&&hour<24&&0<=minute&&minute<60&&0<=second&&second<60)
       {
           this->hour=hour;
           this->minute=minute;
           this->second=second;
       }
    else
        cout<<"Time error!"<<endl;
}

void Clock::showTime() const
{
    cout<<hour<<":"<<minute<<":"<<second<<endl;
}

Clock& Clock::operator ++()
{
    second++;
    if(second>=60)
    {
        second-=60;
        minute++;
        if(minute>=60)
        {
            minute-=60;
            hour=(hour+1)%24;
        }
    return *this;
    }
}

Clock Clock::operator ++(int)
{
    Clock old=*this;
    ++(*this);
    return old;
}

int main()
{
    Clock myClock(23,59,59);
    cout<<"First time output:";
    myClock.showTime();
    cout<<"Show myClock++:   ";
    (myClock++).showTime();
    cout<<"Show ++myClock:   ";
    (++myClock);
    myClock.showTime();
    return 0;
}