采用数组模拟栈，tt模拟栈顶指针

#include<iostream>
using namespace std;
const int N = 1e5 + 10;
int a[N],tt = -1;
string str;
bool isempty(){if (tt == -1)return true;else return false;
}
void push(int x){tt ++;a[tt] = x;
}
void pop(){tt --;
}
void query(){cout << a[tt] <<endl;
}int main(){int n,x;cin >> n;while (n --){cin >> str;if (str == "push"){cin >> x;push(x);}else if (str == "pop"){pop();}else if (str == "empty"){if (isempty())cout <<"YES"<<endl;else cout <<"NO" <<endl;}else if (str == "query"){query();}}
}