c++21行报错，洛谷100分！！！求解

我服了6.4版本c++说c++ 洛谷\P1104.CDD Warning contro end Wreturn-tvoe 结果洛谷提交100分！！！! 6.4版本c++真垃圾

#include <bits/stdc++.h>
using namespace std;
struct node {
    string name;
    int year;
    int month;
    int day;
    int level;
} nn[120];
bool cmp(node a,node b) {
    if(a.year != b.year)
        return a.year < b.year;
    else {
        if(a.month != b.month)
            return a.month < b.month;
        else if(a.day == b.day && a.month == b.month) 
            return a.level > b.level;
        else if(a.day != b.day && a.month == b.month) 
            return a.day < b.day;
    }
}
int main() {
    int n;
    cin>>n;
    for(int i = 1; i <= n; ++i) {
        cin>>nn[i].name>>nn[i].year>>nn[i].month>>nn[i].day;
        nn[i].level = i;
    }
    stable_sort(nn+1,nn+1+n,cmp);
    for(int i = 1; i <= n; ++i) {
        cout<<nn[i].name<<endl;
    }
    return 0;
}

蒟蒻百思不得其解，还请大神来帮忙

一定关注！！！