题解（最简单）

#include<bits/stdc++.h>
using namespace std;
int top;
int a[1010];
//入栈 
void push(int x){
	a[++top]=x;
}
void pop() {
	--top;
}
int Top(){
	return a[top];
}
int size(){
	return top;
}
bool empty(){
	return top==0;
}
int main(){
	int n,x;
    string s;
    cin>>n;
    while(n--){
		cin>>s;
		if(s=="empty"){
			if(empty()) cout<<"yes";
			else cout<<"no";
			cout<<endl;
		}
		else if(s=="push"){
			cin>>x;
			push(x);
		}
		else if(s=="pop"){
			if(!empty()){
                cout<<"pop "<<Top();
                pop();
            }
			else cout<<"pop fail";
			cout<<endl;
		}
		else if(s=="top"){
			if(!empty()) cout<<"top = "<<Top();
			else cout<<"top fail";
			cout<<endl;
		}
		else if(s=="size"){
			cout<<"size = "<<size()<<endl;
		}
		
	}
	return 0;
}