题解 100% AC

#include <bits/stdc++.h>
using namespace std;
int s[110];
int TOP,n;
void push(int x){
    s[++TOP]=x;
}
void pop(){
    --TOP;
}
int top(){
    return s[TOP];
}
bool empty(){
    return TOP==0;
}
int size(){
    return TOP;
}
int main(){
    cin>>n;
    for(int i=1;i<=n;i++){
        string x;
        cin>>x;
        if(x=="push"){
            int a;cin>>a;
            push(a);
        }else if(x=="pop"){
            if(empty()) cout<<"pop fail"<<endl;
            else{
                cout<<"pop "<<top()<<endl;
                pop();
            }
        }else if(x=="top"){
            if(empty()) cout<<"top fail"<<endl;
            else cout<<"top = "<<top()<<endl;
        }else if(x=="size") cout<<"size = "<<size()<<endl;
        else if(x=="empty"){
            if(empty()) cout<<"yes"<<endl;
            else cout<<"no"<<endl;
        }
    }
    return 0;
}