vector模拟栈

#include<bits/stdc++.h>
using namespace std;
vector<int>a;
int n,x;
string s;
int main(){
    cin>>n;
    while(n--){
        cin>>s;
        if(s=="empty"){
            if(a.empty())cout<<"yes"<<endl;
            else cout<<"no"<<endl;
        }
        if(s=="push"){
            cin>>x;
            a.push_back(x);
        }
        if(s=="size"){
            cout<<"size = "<<a.size()<<endl;
        }
        if(s=="pop"){
            if(a.empty())cout<<"pop fail"<<endl;
            else cout<<"pop "<<a[a.size()-1]<<endl,a.pop_back();
        }
        if(s=="top"){
            if(a.empty())cout<<"top fail"<<endl;
            else cout<<"top = "<<a[a.size()-1]<<endl;
        }
    }
    return 0;
}