c++ 日期类 求大神指教

 #include <iostream>
using namespace std;

int maxd(int y, int m)
{
    switch (m)
    {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
        return 31;
    case 2:
        if (y % 4 != 0)
            return 28;
        if (y % 100 == 0 && y % 400 != 0)
            return 28;
        return 29;
    default:
        return 30;
    }
}

class Date{
private:
 int day, month, year;
 static Date default_date; //初始化为 1901年1月1日

public:
 Date(){ day=month=year=0; }
 Date(int d, int m, int y); //构造函数
 int get_day() const; // 返回day
 int get_month() const; //返回month
 int get_year() const; // 返回year
 static void set_default(int, int, int){Date::default_date = Date(1, 1, 1901);} 
 static int get_default_day() {return Date::default_date.get_day();} //返回缺省day
 static int get_default_month(){return Date::default_date.get_month();} //返回缺省month
 static int get_default_year(){return Date::default_date.get_year();} //返回缺省year
 Date& add_year(int n); //加n年
 Date& add_month(int n); //加n月，考虑超过12月，考虑闰年
 Date& add_day(int n); //加n天，考虑进位月和年，考虑闰年
};

Date::Date(int d, int m, int y)
{
    day = d;
    month = m;
    year = y;
}

int Date::get_day() const
{
    return day;
}

int Date::get_month() const
{
    return month;
}

int Date::get_year() const
{
    return year;
}

Date& Date::add_year(int n)
{
    year += n;
    return *this;
}

Date& Date::add_month(int n)
{
    if (month + n <= 12)
    {
        month += n;
        return *this;
    }
    add_year(1);
    n = n - 12 + month;
    month = 1;
    while (n >= 12)
    {
        add_year(1);
        n -= 12;
    }
    month += n;
    return *this;
}

Date& Date::add_day(int n)
{
    if (day + n <= maxd(year, month))
    {
        day += n;
        return *this;
    }
    add_month(1);
    n = n - (maxd(year, month), day) + day;
    day = 1;
    while (n >= maxd(year, month))
    {
        add_month(1);
        n -= maxd(year, month);
    }
    day += n;
    return *this;
}

int main(){

  char type[110];

  int day,mon,year;

  int addday,addmon,addyear;

  while(cin>>type){

      if(strcmp(type,"Date") == 0){

              cin>>day>>mon>>year;

              Date mydate(day,mon,year);

              cin>>addday>>addmon>>addyear;

              mydate.add_day(addday).add_month(addmon).add_year(addyear);

              cout << mydate.get_day() << " " << mydate.get_month() << " " << mydate.get_year() << endl;

      }else if(strcmp(type,"defalutDate") == 0){

              cout << Date::get_default_day() << " " << Date::get_default_month() << " " << Date::get_default_year() << endl;

      }else if(strcmp(type,"setdefaultDate") == 0){

              cin>>day>>mon>>year;

              Date::set_default(day,mon,year);

            cout << Date::get_default_day() << " " << Date::get_default_month() << " " << Date::get_default_year() << endl;

      }

  }

 return 0;

}