Remove all the even digit sum nodes from a doubly linked list

// C Program
// Remove all the even digit sum nodes from a doubly linked list
#include <stdio.h>
#include <stdlib.h>

struct LinkNode
{
	int key;
	struct LinkNode *back;
	struct LinkNode *next;
};
struct DoublyLL
{
	struct LinkNode *front;
	struct LinkNode *rear;
};
// Returns a new linked list
struct DoublyLL *createLinkedList()
{
	struct DoublyLL *dll = (struct DoublyLL *) malloc(sizeof(struct DoublyLL));
	if (dll == NULL)
	{
		printf("\n Memory overflow , When creating a new linked list");
	}
	else
	{
		// Set initial value of linked list
		dll->front = NULL;
		dll->rear = NULL;
	}
	return dll;
}
// Returns a new node of linked list
struct LinkNode *newNode(int key, struct LinkNode *back)
{
	// Create dynamic node
	struct LinkNode *node = (struct LinkNode *) malloc(sizeof(struct LinkNode));
	if (node != NULL)
	{
		node->key = key;
		node->back = back;
		node->next = NULL;
	}
	else
	{
		//This is indicates, segmentation fault or memory overflow problem
		printf("Memory Overflow\n");
	}
	//return new node
	return node;
}
// Handles the request to add new node at the end of linked list
void addNode(struct DoublyLL *dll, int data)
{
	// Create dynamic node
	struct LinkNode *node = newNode(data, dll->rear);
	if (dll->front == NULL)
	{
		dll->front = node;
		dll->rear = node;
	}
	else
	{
		dll->rear->next = node;
	}
	dll->rear = node;
}
// Display linked list element
void display(struct DoublyLL *dll)
{
	if (dll->front == NULL)
	{
		printf("\n Empty linked list\n");
		return;
	}
	printf(" Front to back \n");
	struct LinkNode *temp = dll->front;
	// iterating linked list elements
	while (temp != NULL)
	{
		printf(" %d →", temp->key);
		// Visit to next node
		temp = temp->next;
	}
	printf(" NULL");
	temp = dll->rear;
	printf("\n Back to front\n");
	while (temp != NULL)
	{
		printf(" %d →", temp->key);
		// Visit to back node
		temp = temp->back;
	}
	printf(" NULL\n");
}
// Digit sum 
int digitSum(int num)
{
	int n = num;
	int sum = 0;
	if (n < 0)
	{
		n = -n;
	}
	while (n > 0)
	{
		sum += (n % 10);
		n /= 10;
	}
	// Return sum of each digit
	// Example (123) = 1 + 2 + 3 = 6
	return sum;
}
// Delete all nodes which digit sum is an even value
void deleteEvenDigitSum(struct DoublyLL *dll)
{
	if (dll->front == NULL)
	{
		printf("\n Empty linked list\n");
		return;
	}
	struct LinkNode *temp = NULL;
	struct LinkNode *auxiliary = dll->front;
	// iterate linked list node
	while (auxiliary != NULL)
	{
		if (digitSum(auxiliary->key) % 2 == 0)
		{
			// Get the deleted node
			temp = auxiliary;
			// Visit to next node
			auxiliary = temp->next;
			if (temp == dll->front)
			{
				// When removing first node
				dll->front = auxiliary;
			}
			if (dll->rear == temp)
			{
				// When deleting a last node
				dll->rear = temp->back;
			}
			if (temp->back != NULL)
			{
				temp->back->next = auxiliary;
			}
			if (auxiliary != NULL)
			{
				auxiliary->back = temp->back;
			}
			// Free node
			free(temp);
			temp = NULL;
		}
		else
		{
			// Visit to next node
			auxiliary = auxiliary->next;
		}
	}
}
int main()
{
	struct DoublyLL *dll = createLinkedList();
	addNode(dll, 17);
	addNode(dll, 4);
	addNode(dll, 23);
	addNode(dll, 1);
	addNode(dll, 13);
	addNode(dll, 10);
	printf(" Before Deleting Even digit sum nodes\n");
	// 17 → 4 → 23 → 1 → 13 → 10 → NULL
	display(dll);
	deleteEvenDigitSum(dll);
	printf(" After Delete even digit sum nodes \n");
	//  23 → 1 → 10 → NULL
	display(dll);
	return 0;
}

Output

 Before Deleting Even digit sum nodes
 Front to back
 17 → 4 → 23 → 1 → 13 → 10 → NULL
 Back to front
 10 → 13 → 1 → 23 → 4 → 17 → NULL
 After Delete even digit sum nodes
 Front to back
 23 → 1 → 10 → NULL
 Back to front
 10 → 1 → 23 → NULL