法1

#include<iostream>
#include<algorithm>
#include<cstring>

using namespace std;

int months[13] = {0,31,28,31,30,31,30,31,31,30,31,30,31};

int is_leap(int year)
{
    if(year%4==0 && year%100 || year %400==0)
        return 1;
    return 0;
}

int get_days(int year,int month)//求某月多少天
{
    if(month ==  2) return months[month] + is_leap(year);
    return months[month];
}

int main()
{
    int year,day;
    cin>>year>>day;
    int days = 0;
    for(int i = 0; i<13; i++)
    {
        days += get_days(year,i);
        if(days>=day)
        {
            cout<<i<<endl;
            int t = get_days(year,i)-(days-day);
            cout<<t<<endl;
            break;
        }
    }
}

法2

#include<iostream>
#include<algorithm>
#include<cstring>

using namespace std;

int months[13] = {0,31,28,31,30,31,30,31,31,30,31,30,31};

int is_leap(int year)
{
    if(year%4==0 && year%100 || year %400==0)
        return 1;
    return 0;
}

int get_days(int year,int month)//求某月多少天
{
    if(month ==  2) return months[month] + is_leap(year);
    return months[month];
}

int main()
{
    int year,d;
    cin>>year>>d;
    for(int i = 1; i<=12; i++)
        for(int j = 1; j<=get_days(year,i); j++)
        {
            if(--d==0)
            {
                printf("%d\n%d\n",i,j);
                return 0;
            }
        }
    return 0;
}