题解

#include <bits/stdc++.h>
#include <stack>
using namespace std;
stack<int>st;
int main(){
	int n;
    string s;
    cin>>n;
    while(n--){
		cin>>s;
        if(s=="push"){
            int k;
            cin>>k;
            st.push(k);
        }
        else if(s=="top"){
			if(st.empty()==true)  cout<<"top fail\n";
            else cout<<"top = "<<st.top()<<endl;
        }
        else if(s=="size"){
			cout<<"size = "<<st.size()<<endl;
        }
        else if(s=="empty"){
			if(st.empty()==true) cout<<"yes\n";
            else cout<<"no\n";
        }
        else if(s=="pop"){
			if(st.empty()==true) cout<<"pop fail\n";
            else{
				cout<<"pop "<<st.top()<<endl;
                st.pop();
            }
        }
    }
	
	return 0;
}