#include<iostream> #include<string> using namespace std; const int N = 100000; int main() { int stk[N], tt = 0;//tt表示栈顶 int n, x; string sb; cin >> n; while (n--) { cin >> sb; if (sb == "push") { cin >> x; stk[++tt] = x;//向栈顶插入一个数 } if (sb == "pop") { if (tt <= 0) {//判断栈是否为空,如果tt>0,则表示不为空 cout << "error" << endl; continue; } cout << stk[tt] << endl; tt--;//从栈顶弹出一个数 } if (sb == "top") { if (tt <= 0) { cout << "error" << endl; continue; } cout << stk[tt] << endl; } } return 0; }