Queue

// CPP program for array
// implementation of queue
#include <bits/stdc++.h>
using namespace std;
 
// A structure to represent a queue
class Queue {
public:
    int front, rear, size;
    unsigned capacity;
    int* array;
};
 
// function to create a queue
// of given capacity.
// It initializes size of queue as 0
Queue* createQueue(unsigned capacity)
{
    Queue* queue = new Queue();
    queue->capacity = capacity;
    queue->front = queue->size = 0;
 
    // This is important, see the enqueue
    queue->rear = capacity - 1;
    queue->array = new int[queue->capacity];
    return queue;
}
 
// Queue is full when size
// becomes equal to the capacity
int isFull(Queue* queue)
{
    return (queue->size == queue->capacity);
}
 
// Queue is empty when size is 0
int isEmpty(Queue* queue)
{
    return (queue->size == 0);
}
 
// Function to add an item to the queue.
// It changes rear and size
void enqueue(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;
    cout << item << " enqueued to queue
";
}
 
// Function to remove an item from queue.
// It changes front and size
int dequeue(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(Queue* queue)
{
    if (isEmpty(queue))
        return INT_MIN;
    return queue->array[queue->front];
}
 
// Function to get rear of queue
int rear(Queue* queue)
{
    if (isEmpty(queue))
        return INT_MIN;
    return queue->array[queue->rear];
}
 
// Driver code
int main()
{
    Queue* queue = createQueue(1000);
 
    enqueue(queue, 10);
    enqueue(queue, 20);
    enqueue(queue, 30);
    enqueue(queue, 40);
 
    cout << dequeue(queue)
         << " dequeued from queue
";
 
    cout << "Front item is "
         << front(queue) << endl;
    cout << "Rear item is "
         << rear(queue) << endl;
 
    return 0;
}