Print node from backward and forward direction of doubly linked list in c

C program for Print node from backward and forward direction of doubly linked list. Here problem description and explanation.

// Include header file
#include <stdio.h>
#include <stdlib.h>
/* 
  C program for
  Print node in forward and backward direction 
  in doubly linked list
*/
typedef struct LinkNode
{
	// Define useful field of LinkNode
	int key;
	struct LinkNode * next;
	struct LinkNode * back;
}LinkNode;

LinkNode * getLinkNode(int key)
{
	// Create dynamic memory of LinkNode
	LinkNode * ref = (LinkNode * ) malloc(sizeof(LinkNode));
	if (ref == NULL)
	{
		// Failed to create memory 
		return NULL;
	}
	// Setup initial values of node
	ref->key = key;
	ref->next = NULL;
	ref->back = NULL;
	return ref;
}

typedef struct DoublyLL
{
	// Define useful field of DoublyLL
	struct LinkNode * front;
	struct LinkNode * rear;
}DoublyLL;

DoublyLL * getDoublyLL()
{
	// Create dynamic memory of DoublyLL
	DoublyLL * ref = (DoublyLL * ) malloc(sizeof(DoublyLL));
	if (ref == NULL)
	{
		// Failed to create memory 
		return NULL;
	}
	// Set initial default value
	ref->front = NULL;
	ref->rear = NULL;
	return ref;
}
void addNode(DoublyLL * ref, int value)
{
	// Create a new node
	LinkNode * node = getLinkNode(value);
	if ((ref->front == NULL))
	{
		ref->front = node;
	}
	else
	{
		// Add Node at the end of linked list
		node->back = ref->rear;
		ref->rear->next = node;
	}
	// New last node
	ref->rear = node;
}
// Print linked list node from left to right 
// Forward direction
void forwardDirection(DoublyLL * ref)
{
	if ((ref->front == NULL))
	{
		printf("\n Empty linked list");
		return;
	}
	printf("\n Forward Direction Nodes\n");
	LinkNode * temp = ref->front;
	// iterating linked list elements
	while (temp != NULL)
	{
		// Display node value
		printf(" %d ", temp->key);
		// Visit to next node
		temp = temp->next;
	}
}
// Print linked list node from right to left 
// Backward direction
void backwardDirection(DoublyLL * ref)
{
	if ((ref->rear == NULL))
	{
		printf("\n Empty linked list");
		return;
	}
	printf("\n Backward Direction Nodes\n");
	// In case last node unknown then first find last node
	LinkNode * temp = ref->rear;
	// iterating linked list elements
	while (temp != NULL)
	{
		// Display node value
		printf(" %d ", temp->key);
		// Visit to previous node
		temp = temp->back;
	}
}
int main()
{
	DoublyLL * dll = getDoublyLL();
	// Add nodes
	addNode(dll, 24);
	addNode(dll, 4);
	addNode(dll, 21);
	addNode(dll, 10);
	addNode(dll, 13);
	addNode(dll, 15);
	addNode(dll, 28);
	// Constructing linked list
	// NULL ← 24 ⟷ 4 ⟷ 21 ⟷ 10 ⟷ 13 ⟷ 15 ⟷ 28 → NULL
	//         ↑                            ↑
	//         head                        rear
	forwardDirection(dll);
	backwardDirection(dll);
}

Output

 Forward Direction Nodes
 24  4  21  10  13  15  28
 Backward Direction Nodes
 28  15  13  10  21  4  24