有谁和我一样用std::vector

#include<iostream>
#include <ostream> //不知何时加进来的（#include <...>不想我的风格）
#include<vector>
std::istream& is=std::cin;
std::ostream& os=std::cout;
typedef std::string str;
using array=std::vector<int64_t>;
using std::endl;
int main(){
    int64_t n;
    is>>n;
    array arr;
    while(n--){
        str func;
        is>>func;
        if(func=="push"){
            int64_t num;
            is>>num;
            arr.push_back(num);
        }else if(func=="pop"){
            if(arr.empty())os<<"pop fail"<<endl;
            else{
                os<<"pop "<<arr.back()<<endl;
                arr.pop_back();
            }
        }else if(func=="top"){
            if(arr.empty())os<<"top fail"<<endl;
            else os<<"top = "<<arr.back()<<endl;
        }else if(func=="size")os<<"size = "<<arr.size()<<endl;
        else if(func=="empty")os<<(arr.empty()?"yes":"no")<<endl;
    }
}