Circular Queue in C

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

#define SIZE 6

struct Queue
{
  int front, rear, currSize;
  unsigned maxSize;
  int *a;
};

struct Queue *createQueue (unsigned maxSize)
{
  struct Queue *queue = (struct Queue *) malloc (sizeof (struct Queue));
  queue->maxSize = maxSize;
  queue->front = queue->rear = -1;
  queue->a = (int *) malloc (queue->maxSize * sizeof (int));
  return queue;
}

// Checking for Overflow condition
int isFull (struct Queue *queue)
{
  if ((queue->front == queue->rear + 1) ||
      (queue->front == 0 && queue->rear == queue->maxSize - 1))
    {
      return 1;
    }
  return 0;
}

// Checking for Underflow condition
int isEmpty (struct Queue *queue)
{
  if (queue->front == -1)
    {
      return 1;
    }
  return 0;
}

// Function to do enqueue
void enqueue (struct Queue *queue, int value)
{
  if (isFull (queue))
    printf ("Can't add the queue is full \n");

  else
    {
      if (queue->front == -1)
	queue->front = 0;

      queue->rear = (queue->rear + 1) % queue->maxSize;
      queue->a[queue->rear] = value;
      printf ("%d was added\n", value);
    }
}

// Function to do dequeue
int dequeue (struct Queue *queue)
{
  int item;
  if (isEmpty (queue))
    {
      printf ("Can't add the queue is empty \n");
      return (-1);
    }
  else
    {
      item = queue->a[queue->front];
      if (queue->front == queue->rear)
	{
	  queue->front = queue->rear = -1;
	}
      else
	{
	  queue->front = (queue->front + 1) % queue->maxSize;
	}
      printf ("%d dequeued\n", item);
    }
}

// Function to print the queue
void print (struct Queue *queue)
{
  int i;
  if (isEmpty (queue))
    printf ("Empty Queue\n");
  else
    {

      printf ("\nThe items in the queue are : \n");
      for (i = queue->front; i != queue->rear; i = (i + 1) % queue->maxSize)
	{
	  printf ("%d ", queue->a[i]);
	}
      printf ("%d \n\n", queue->a[i]);

    }
}

int main ()
{
  struct Queue *queue = createQueue (6);
  dequeue (queue);		//Underflow condition

  enqueue (queue, 12);
  enqueue (queue, 14);
  enqueue (queue, 16);
  enqueue (queue, 18);
  enqueue (queue, 20);

  print (queue);
  dequeue (queue);
  dequeue (queue);

  print (queue);

  enqueue (queue, 22);
  enqueue (queue, 24);
  enqueue (queue, 26);
  enqueue (queue, 28);		//Overflow condition
  print (queue);

  return 0;
}