Queue in C/C++

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// C program for array implementation of queue
/*
Enqueue: Adds an item to the queue. If the queue is full, then it is said to be an Overflow condition.
Dequeue: Removes an item from the queue. The items are popped in the same order in which they are pushed. If the queue is empty, then it is said to be an Underflow condition.
Front: Get the front item from queue.
Rear: Get the last item from queue.
*/
#include <stdio.h>
#include <stdlib.h>
#include <limits.h>
// A structure to represent a queue
struct Queue
{
    int front, rear, size;
    unsigned capacity;
    int* array;
};
// function to create a queue of given capacity.
// It initializes size of queue as 0
struct Queue* createQueue(unsigned capacity)
{
    struct Queue* queue = (struct Queue*) malloc(sizeof(struct Queue));
    queue->capacity = capacity;
    queue->front = queue->size = 0;
    queue->rear = capacity - 1;  // This is important, see the enqueue
    queue->array = (int*) malloc(queue->capacity * sizeof(int));
    return queue;
}
// Queue is full when size becomes equal to the capacity
int isFull(struct Queue* queue)
{  return (queue->size == queue->capacity);  }
// Queue is empty when size is 0
int isEmpty(struct Queue* queue)
{  return (queue->size == 0); }
// Function to add an item to the queue.
// It changes rear and size
void enqueue(struct Queue* queue, int item)
{
    if (isFull(queue))
        return;
    queue->rear = (queue->rear + 1)%queue->capacity;
    queue->array[queue->rear] = item;
    queue->size = queue->size + 1;
    printf("%d enqueued to queue\n", item);
}
// Function to remove an item from queue.
// It changes front and size
int dequeue(struct Queue* queue)
{
    if (isEmpty(queue))
        return INT_MIN;
    int item = queue->array[queue->front];
    queue->front = (queue->front + 1)%queue->capacity;
    queue->size = queue->size - 1;
    return item;
}
// Function to get front of queue
int front(struct Queue* queue)
{
    if (isEmpty(queue))
        return INT_MIN;
    return queue->array[queue->front];
}
// Function to get rear of queue
int rear(struct Queue* queue)
{
    if (isEmpty(queue))
        return INT_MIN;
    return queue->array[queue->rear];
}
// Driver program to test above functions./
int main()
{
    struct Queue* queue = createQueue(1000);
    enqueue(queue, 10);
    enqueue(queue, 20);
    enqueue(queue, 30);
    enqueue(queue, 40);
    printf("%d dequeued from queue\n", dequeue(queue));
    printf("Front item is %d\n", front(queue));
    printf("Rear item is %d\n", rear(queue));
    return 0;
}

/*
The functions supported by queue are :
empty() – Returns whether the queue is empty
size() – Returns the size of the queue
front() – Returns a reference to the first element of the queue
back() – Returns a reference to the last element of the queue
push(g) – Adds the element ‘g’ at the end of the queue
pop() – Deletes the first element of the queue
*/
#include <iostream>
#include <queue>
using namespace std;
void showq(queue <int> gq)
{
    queue <int> g = gq;
    while (!g.empty())
    {
        cout << '\t' << g.front();
        g.pop();
    }
    cout << '\n';
}
int main()
{
    queue <int> gquiz;
    gquiz.push(10);
    gquiz.push(20);
    cout << "The queue gquiz is : ";
    showq(gquiz);
    cout << "\ngquiz.size() : " << gquiz.size();
    cout << "\ngquiz.front() : " << gquiz.front();
    cout << "\ngquiz.back() : " << gquiz.back();
    cout << "\ngquiz.pop() : ";
    gquiz.pop();
    showq(gquiz);
    return 0;
}