复制粘贴就能过

无注释版

#include <iostream>
using namespace std;

int main(){
    int year, month;
    cin >> year >> month;
    if (month == 2){
        if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
            cout << "29";
        }else{
            cout << "28";
        }
    }else{
        switch (month) {
            case 1:
            case 3:
            case 5:
            case 7:
            case 8:
            case 10:
            case 12:cout << "31";break;
            default:cout << "30";
        }
    }
}

简单的if else和switch