queue.c

// C program for array implementation of queue
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>

#include "queue.h"

// 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;

    // This is important, see the enqueue
    queue->rear = capacity - 1;
    queue->array = (int *)malloc(
        queue->capacity * sizeof(int));
    return queue;
}

void destroyQueue(struct Queue *queue)
{
    free(queue->array);
    free(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;
}

// 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\n",
//            dequeue(queue));

//     printf("Front item is %d\n", front(queue));
//     printf("Rear item is %d\n", rear(queue));

//     return 0;
// }