思路

先判断闰年，然后通过是否是闰年判断2月份有多少天，其他的都正常

#include<iostream>
using namespace std;

int main()
{
    int y, m;
    cin >> y >> m;
    bool isCommon;
    //先判断是否是闰年
    if(y % 4 == 0 && y % 100 != 0 || y % 400 == 0)
    {
        isCommon = false;
    }
    else
    {
        isCommon = true;
    }

    switch(m)
    {
        case 1:
            cout << 31;
            break;
        case 2:
            if(isCommon) cout << 28;
            else cout << 29;
            break;
        case 3:
            cout << 31;
            break;
        case 4:
            cout << 30;
            break;
        case 5:
            cout << 31;
            break;
        case 6:
            cout << 30;
            break;
        case 7:
            cout << 31;
            break;
        case 8:
            cout << 31;
            break;
        case 9:
            cout << 30;
            break;
        case 10:
            cout << 31;
            break;
        case 11:
            cout << 30;
            break;
        case 12:
            cout << 31;
            break;
    }
    return 0;
}