1.题目：

 

2.分析：

见代码。

3.我的代码：

#include <iostream>
using namespace std;

class Date 
{
public:
    Date(int year = 1)
    : _year(year) {}

    inline int GetMonthDay(int year, int month) 
    {
        static int arr[13] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
        if ((month == 2) && ((year % 400 == 0) || ((year % 4 == 0) && (year % 100 != 0))))
        {
            return 29;
        }
        else 
        {
            return arr[month];
        }
    }

    void ShowDate(int addDay)
    {
        _day = addDay;
        while (_day > GetMonthDay(_year, _month))
        {
            _day -= GetMonthDay(_year, _month);
            ++_month;
            if (_month > 12)
            {
                _month -= 12;
                ++_year;
            }
        }
        if (_month < 10 && _day < 10)
        {
            cout << _year << "-0" << _month << "-0" << _day << endl;
        }
        else if (_month < 10 && _day >= 10)
        {
            cout << _year << "-0" << _month << "-" << _day << endl;
        }
        else if (_month >= 10 && _day < 10)
        {
            cout << _year << "-" << _month << "-0" << _day << endl;
        }
        else
        {
            cout << _year << "-" << _month << "-" << _day << endl;
        }
    }
private:
    int _year = 1;
    int _month = 1;
    int _day = 1;
};
int main() 
{
    int year = 0;
    int addDay = 0;
    cin >> year >> addDay;
    Date date(year);
    date.ShowDate(addDay);
}

4.答案代码：

#include <iostream>

  using namespace std;

   

  int main()

  {

    int year;

    int day;

     

    int mon[13] = {31, 28, 31, 30, 31, 30, 31, 31, 30 ,31, 30, 31};   

    while(cin>>year>>day)

    {

      if(((year % 4 == 0) && (year % 100 != 0)) || (year % 400 == 0))

        mon[1] = 29;

      else

        mon[1] = 28;

        

      for(int i = 0; i < 12; i++)

      {

        if(day <= mon[i])

        {

          printf("%04d-%02d-%02d\n", year, i + 1, day);

          break;

        }

        else

        {

        day = day - mon[i];

        }

    }

    }

    return 0;

  }