[10845번] QUEUE 큐 - Queue [C++]

https://www.acmicpc.net/problem/10845

#include <queue>
#include <stdio.h>
#include <iostream>
#include <string>
 
using namespace std;
 
int main() {
    int N;
    cin >> N;
    string input;
    queue<int> q;
    for (int i = 0; i < N; i++) {
        cin >> input;
        if (input == "push") {            //push
            int num;
            cin >> num;
            q.push(num);
            //printf("%d\n", num); No print, if push.
        }
        else if (input == "front") {    //front
            if (q.empty() == 1)
                printf("-1\n");
            else
                printf("%d\n", q.front());
        }
        else if (input == "back") {        //back
            if (q.empty() == 1) {
                printf("-1\n");
            else
                printf("%d\n", q.back());
        }
        else if (input == "size")        //size
            printf("%d\n", q.size());
        else if (input == "pop") {        //pop
            if (q.empty() == 1)
                printf("-1\n");
            else {
                printf("%d\n", q.front());
                q.pop();
            }
        }
        else if (input == "empty")        //empty
            printf("%d\n", q.empty());
    }
    return 0;
}