queue in c

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

#define TRUE  1
#define FALSE	0

/* a link in the queue, holds the info and point to the next Node*/
typedef struct {
    int info;
} DATA;

typedef struct Node_t {
    DATA data;
    struct Node_t *prev;
} NODE;

/* the HEAD of the Queue, hold the amount of node's that are in the queue*/
typedef struct Queue {
    NODE *head;
    NODE *tail;
    int size;
    int limit;
} Queue;

Queue *ConstructQueue(int limit);
void DestructQueue(Queue *queue);
int Enqueue(Queue *pQueue, NODE *item);
NODE *Dequeue(Queue *pQueue);
int isEmpty(Queue* pQueue);

Queue *ConstructQueue(int limit) {
    Queue *queue = (Queue*) malloc(sizeof (Queue));
    if (queue == NULL) {
        return NULL;
    }
    if (limit <= 0) {
        limit = 65535;
    }
    queue->limit = limit;
    queue->size = 0;
    queue->head = NULL;
    queue->tail = NULL;

    return queue;
}

void DestructQueue(Queue *queue) {
    NODE *pN;
    while (!isEmpty(queue)) {
        pN = Dequeue(queue);
        free(pN);
    }
    free(queue);
}

int Enqueue(Queue *pQueue, NODE *item) {
    /* Bad parameter */
    if ((pQueue == NULL) || (item == NULL)) {
        return FALSE;
    }
    // if(pQueue->limit != 0)
    if (pQueue->size >= pQueue->limit) {
        return FALSE;
    }
    /*the queue is empty*/
    item->prev = NULL;
    if (pQueue->size == 0) {
        pQueue->head = item;
        pQueue->tail = item;

    } else {
        /*adding item to the end of the queue*/
        pQueue->tail->prev = item;
        pQueue->tail = item;
    }
    pQueue->size++;
    return TRUE;
}

NODE * Dequeue(Queue *pQueue) {
    /*the queue is empty or bad param*/
    NODE *item;
    if (isEmpty(pQueue))
        return NULL;
    item = pQueue->head;
    pQueue->head = (pQueue->head)->prev;
    pQueue->size--;
    return item;
}

int isEmpty(Queue* pQueue) {
    if (pQueue == NULL) {
        return FALSE;
    }
    if (pQueue->size == 0) {
        return TRUE;
    } else {
        return FALSE;
    }
}

int main() {
    int i;
    Queue *pQ = ConstructQueue(7);
    NODE *pN;

    for (i = 0; i < 9; i++) {
        pN = (NODE*) malloc(sizeof (NODE));
        pN->data.info = 100 + i;
        Enqueue(pQ, pN);
    }

    while (!isEmpty(pQ)) {
        pN = Dequeue(pQ);
        printf("\nDequeued: %d", pN->data);
        free(pN);
    }
    DestructQueue(pQ);
    return (EXIT_SUCCESS);
}// Circular Queue implementation in C

#include <stdio.h>

#define SIZE 5

int items[SIZE];
int front = -1, rear = -1;

// Check if the queue is full
int isFull() {
  if ((front == rear + 1) || (front == 0 && rear == SIZE - 1)) return 1;
  return 0;
}

// Check if the queue is empty
int isEmpty() {
  if (front == -1) return 1;
  return 0;
}

// Adding an element
void enQueue(int element) {
  if (isFull())
    printf("\n Queue is full!! \n");
  else {
    if (front == -1) front = 0;
    rear = (rear + 1) % SIZE;
    items[rear] = element;
    printf("\n Inserted -> %d", element);
  }
}

// Removing an element
int deQueue() {
  int element;
  if (isEmpty()) {
    printf("\n Queue is empty !! \n");
    return (-1);
  } else {
    element = items[front];
    if (front == rear) {
      front = -1;
      rear = -1;
    } 
    // Q has only one element, so we reset the 
    // queue after dequeing it. ?
    else {
      front = (front + 1) % SIZE;
    }
    printf("\n Deleted element -> %d \n", element);
    return (element);
  }
}

// Display the queue
void display() {
  int i;
  if (isEmpty())
    printf(" \n Empty Queue\n");
  else {
    printf("\n Front -> %d ", front);
    printf("\n Items -> ");
    for (i = front; i != rear; i = (i + 1) % SIZE) {
      printf("%d ", items[i]);
    }
    printf("%d ", items[i]);
    printf("\n Rear -> %d \n", rear);
  }
}

int main() {
  // Fails because front = -1
  deQueue();

  enQueue(1);
  enQueue(2);
  enQueue(3);
  enQueue(4);
  enQueue(5);

  // Fails to enqueue because front == 0 && rear == SIZE - 1
  enQueue(6);

  display();
  deQueue();

  display();

  enQueue(7);
  display();

  // Fails to enqueue because front == rear + 1
  enQueue(8);

  return 0;
}// Circular Queue implementation in C

#include <stdio.h>

#define SIZE 5

int items[SIZE];
int front = -1, rear = -1;

// Check if the queue is full
int isFull() {
  if ((front == rear + 1) || (front == 0 && rear == SIZE - 1)) return 1;
  return 0;
}

// Check if the queue is empty
int isEmpty() {
  if (front == -1) return 1;
  return 0;
}

// Adding an element
void enQueue(int element) {
  if (isFull())
    printf("\n Queue is full!! \n");
  else {
    if (front == -1) front = 0;
    rear = (rear + 1) % SIZE;
    items[rear] = element;
    printf("\n Inserted -> %d", element);
  }
}

// Removing an element
int deQueue() {
  int element;
  if (isEmpty()) {
    printf("\n Queue is empty !! \n");
    return (-1);
  } else {
    element = items[front];
    if (front == rear) {
      front = -1;
      rear = -1;
    } 
    // Q has only one element, so we reset the 
    // queue after dequeing it. ?
    else {
      front = (front + 1) % SIZE;
    }
    printf("\n Deleted element -> %d \n", element);
    return (element);
  }
}

// Display the queue
void display() {
  int i;
  if (isEmpty())
    printf(" \n Empty Queue\n");
  else {
    printf("\n Front -> %d ", front);
    printf("\n Items -> ");
    for (i = front; i != rear; i = (i + 1) % SIZE) {
      printf("%d ", items[i]);
    }
    printf("%d ", items[i]);
    printf("\n Rear -> %d \n", rear);
  }
}

int main() {
  // Fails because front = -1
  deQueue();

  enQueue(1);
  enQueue(2);
  enQueue(3);
  enQueue(4);
  enQueue(5);

  // Fails to enqueue because front == 0 && rear == SIZE - 1
  enQueue(6);

  display();
  deQueue();

  display();

  enQueue(7);
  display();

  // Fails to enqueue because front == rear + 1
  enQueue(8);

  return 0;
}