我这有什么问题吗??!! 有个测试点明明输出和答案一样, 它还WA!!!

#include <iostream>

using namespace std;

const int N =  100010;
int QuickStack[N];

int head;

void push(int x){ QuickStack[++ head] = x; }

void pop(){ head --; }

bool empty(){ return head == 0; }

int query(){ return QuickStack[head]; }

int main()
{
    ios :: sync_with_stdio(false),
    cin.tie(0), 
    cout.tie(0);

    int n;

    cin >> n;
    while(n --){
        string que;
        int x;

        cin >> que;

        if(que == "push") cin >> x, push(x);
        else if(que == "pop") pop();
        else if(que == "query") cout << query() << endl;
        else cout << (empty() ? "Yes" : "No") << endl;
    }

    return 0;
}