queue.h

#include <stdlib.h>
#include <stdio.h>

// A linked list (LL) node to store a queue entry
struct QNode
{
	int key;
	struct QNode *next;
};

// The queue, front stores the front node of LL and rear stores ths
// last node of LL
struct Queue
{
	struct QNode *front, *rear;
};

// A utility function to create a new linked list node.
struct QNode* newNode(int k)
{
	struct QNode *temp = (struct QNode*)malloc(sizeof(struct QNode));
	temp->key = k;
	temp->next = NULL;
	return temp;
}

// A utility function to create an empty queue
struct Queue *createQueue()
{
	struct Queue *q = (struct Queue*)malloc(sizeof(struct Queue));
	q->front = q->rear = NULL;
	return q;
}

// The function to add a key k to q
void enQueue(struct Queue *q, int k)
{
	// Create a new LL node
	struct QNode *temp = newNode(k);

	// If queue is empty, then new node is front and rear both
	if (q->rear == NULL)
	{
	q->front = q->rear = temp;
	return;
	}

	// Add the new node at the end of queue and change rear
	q->rear->next = temp;
	q->rear = temp;
}

// Function to remove a key from given queue q
struct QNode *deQueue(struct Queue *q)
{
	// If queue is empty, return NULL.
	if (q->front == NULL)
	return NULL;

	// Store previous front and move front one node ahead
	struct QNode *temp = q->front;
	q->front = q->front->next;

	// If front becomes NULL, then change rear also as NULL
	if (q->front == NULL)
	q->rear = NULL;
	return temp;
}

void printQueue(struct Queue *q)
{
	if (q->front == NULL)
	{
		printf("Write Queue Empty\n");
		return;
	}
	printf("[");
	struct Queue *tempq = q;
	struct QNode *tempn = tempq->front;
	int f=0;
	while(f==0)
	{
		printf(" %d ",tempn->key);
		if(tempn->next == 0)
			break;
		tempn=tempn->next;
	}
	printf("]\n");
	return;
}

int isQueueEmpty(struct Queue *q)
{
	if (q->front == NULL)
		return 1;
    else
        return 0;
}