This is a simple queue implementation (both array and linked list based) that I created in class.

Queue.cc

#include <iostream>
using namespace std;

//A queue is a FIFO (first-in-first-out data structure

const int SIZE = 5;

class QueueA {
    private:
    int data[SIZE];
    int front;
    int back;
    void inc(int& x) {//increment
        x++;
        if (x >= SIZE)
            x = 0;
        //equivalent: (x+1)%SIZE
    }

    public:
    QueueA() {
        front = 0;  //index of the next element to dequeue
        back = 0;  //index of the next element to add something
    }
    bool enq(int x) {
        if (full())
            return false;
        data[back] = x;
        inc(back);
        return true;
    }
    bool deq(int& x) {
        if (back == front)  //if empty
            return false;
        x = data[front];
        inc(front);
        return true;
    }
    bool full() {
        int b2 = back;
        inc(b2);
        if (b2 == front)
            return true;
        else
            return false;
    }
    bool empty() {
        return (back == front) ? true : false;
    }
};

class QueueLL {
    private:
    struct Node {
        int data;
        Node* next;
    };
    Node* front;
    Node* back;

    public:
    QueueLL() {
        front = NULL;
        back = NULL;
    }
    void enq(int x) {
        Node* nn = new Node;
        nn->data = x;
        nn->next = NULL;
        if (back != NULL)
            back->next = nn;
        back = nn;
        if (front == NULL)
            front = nn;
    }
    bool deq(int& x) {
        if (front == NULL)
            return false;
        x = front->data;
        Node* n2d = front;  //node to delete
        front = front->next;
        delete n2d;
        if (front == NULL)
            back = NULL;
        return true;
    }
};

int main() {
    QueueLL test;
    test.enq(5);
    test.enq(7);
    test.enq(9);
    test.enq(10);
    int x;
    for (int i = 0; i < 4; i++)
    {
        test.deq(x);
        cout << x << endl;
    }
}