关于输出日期出错：function call missing argument list？？？

#include "iostream.h"
#include "string.h"


class date
{    
    int Year;
    int Month;
    int Day;
    bool flag;
public:
    date()
    {
        Year=0;
        Month=0;
        Day=0;
    
    }
 
    date (int year, int mon, int day);
    void setdate();
    int getyear();
    int getmonth();
    int getday();
    void addday();
    void show();

};

date::date(int year,int mon,int day)
{    flag=false;
    if(mon>=1&&mon<=12&&day>=1&&day<=31)
    {
        Year=year;
        Month=mon;
        Day=day;
    }
    else
    {
        flag=true;
    }

}

void date::setdate()
{    
    cout<<"请输入年份"<<endl;
    cin>>Year;

    cout<<"请输入月份(1-12)"<<endl;
    cin>>Month;
    while(Month<1||Month>12)
    {    
        cout<<"输入有误，请重新输入"<<endl;
        cin>>Month;
    }

    cout<<"请输入日期"<<endl;
    cin>>Day;
    while(Day<1||Day>31)
    {
        cout<<"输入有误，请重新输入"<<endl;
        cin>>Day;
    
    }
     
    flag=false;
 

}






void date::show()
{
    cout<<Year<<'/'<<Month<<'/'<< Day <<endl;
}




int date::getyear()
{
    return Year;
}

int date::getmonth()
{
    return Month;
}

int date::getday()
{
    return Day;
}



void date::addday()
{
    Day++;
    if(Month==2)
    {
        bool leapyear;
        leapyear=((Year%400==0)||((Year%100!=0)&&(Year%4==0)));
        if (leapyear)
        {
            if(Day>29)
            {
                Day=1;
                Month++;
                
            }
        }
        else
        {
            if(Day>28)
            {
                Day=1;
                Month++;
            }
        }
        
    } 
    else if(Month==1||Month==3||Month==5||Month==7||Month==8||Month==10||Month==12)
    {
        if (Day>31)
        {
            Day=1;
            Month++;
        }
    }

    else
    {
        if(Day>30)
        {
            Day=1;
            Month++;
        }
    
    }
    if(Month==12)
    {
        Month=1;
        Year++;
    }
    
    
    
    
}


void main()
{    
    date d1(1998,12,4);
    d1.show();
    d1.setdate();
    d1.show();
    cout<<"日期增加一天结果为："<<endl;
    d1.addday;
    d1.show();

}