最简单

#include <bits/stdc++.h>
using namespace std;
stack<int>s;
int main(){
int n;
int x;
cin >> n;
for(int i = 1;i<=n;i++){
string m;
cin >> m;
if(m=="empty"){
if(s.empty()){
cout << "yes" << endl;
}else{
cout << "no" << endl;
}

    }else if(m=="push"){
        cin >> x;
        
        s.push(x);
    }else if(m=="size"){
        cout << "size = "<<s.size() << endl;
    }else if(m=="top"){
        if(s.empty()){
            cout << "top fail " << endl;
        }else{
            cout << "top = " << s.top() << endl;
        }
    }else{
        if(s.empty()){
            cout << "pop fail " << endl;
        }else{
            cout << "pop "<<s.top()<<endl;
            s.pop();
        }
        
    }
}
return 0;

}