Simple Stack

#include <bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    int x;
    stack<int> my;
    while(cin >> s){
        if(s == "exit"){
            cout << "bye" << endl;
            break;
        }
        if(s == "push"){
            cin >> x;
            my.push(x);
            cout << "ok" << endl;
        }
        if(s == "pop"){
            cout << my.top() << endl;
            my.pop();
        }
        if(s == "back"){
            cout << my.top() << endl;
        }
        if(s == "size"){
            cout << my.size() << endl;
        }
        if(s == "clear"){
            while(!my.empty()){
                my.pop();
            }
            cout << "ok" << endl;
        }
    }
}