Find sum and product of prime nodes in linked list

// C Program 
// Find sum and product of prime nodes in linked list
#include <stdio.h>

#include <stdlib.h> //for malloc function

//Linked List Node
struct Node
{
	int data;
	struct Node *next;
};
//Create a node of linked list
struct Node *create_node(int data)
{
	//Create dynamic node
	struct Node *node = (struct Node *) malloc(sizeof(struct Node));
	if (node == NULL)
	{
		printf("Memory overflow\n");
	}
	else
	{
		//Set initial node value
		node->data = data;
		node->next = NULL;
	}
	return node;
}
//Add new node at end of linked list 
void add_node(struct Node **head, int data)
{
	struct Node *node = create_node(data);
	if ( *head == NULL)
	{
		*head = node;
	}
	else
	{
		struct Node *temp = *head;
		//Find last node
		while (temp->next != NULL)
		{
			temp = temp->next;
		}
		//Add node at last possition
		temp->next = node;
	}
}
//Display linked list element
void display(struct Node *head)
{
	if (head == NULL)
	{
		printf("\nEmpty linked list\n");
		return;
	}
	struct Node *temp = head;
	//iterating linked list elements
	while (temp != NULL)
	{
		if (temp != head)
		{
			printf(" →");
		}
		printf(" %d", temp->data);
		//visit to next node
		temp = temp->next;
	}
	printf(" → NULL\n");
}
//Check that whether given number is prime or not
int is_prime(int num)
{
	if (num == 2 || num == 3 || num == 5)
	{
		return 1;
	}
	if (num <= 1 || (num % 2 == 0) || (num % 3 == 0) || (num % 5 == 0))
	{
		return 0;
	}
	int i = 11;
	while ((i *i) <= num)
	{
		if (num % i == 0)
		{
			//When number is divisible of current i value
			return 0;
		}
		else if (num % (i + 2) == 0)
		{
			//When number is divisible of current i + 2 value
			return 0;
		}
		i = i + 6;
	}
	return 1;
}
//Calculate sum and product of prime node values in linked list
void find_sum_product(struct Node *head)
{
	if (head == NULL)
	{
		printf("\nEmpty linked List");
	}
	else
	{
		// Define some useful resultant variables
		struct Node *auxiliary = head;
		// Define usful resultant variables
		int sum = 0;
		int product = 1;
		int find = 0;
		// iterating linked list elements
		while (auxiliary != NULL)
		{
			//Check node value is prime or not
			if (is_prime(auxiliary->data))
			{
				//Active the find of prime nodes
				find = 1;
				//Calculating the sum of prime node value
				sum += auxiliary->data;
				product *= auxiliary->data;
			}
			// Visit to next node
			auxiliary = auxiliary->next;
		}
		if (find == 0)
		{
			printf("\n Prime node not exists");
		}
		else
		{
			//Display result
			printf(" Prime Sum     : %d", sum);
			printf("\n Prime Product : %d\n", product);
		}
	}
}
int main()
{
	struct Node *head = NULL;
	//Add linked list node
	add_node( &head, 2);
	add_node( &head, 9);
	add_node( &head, 1);
	add_node( &head, 5);
	add_node( &head, 6);
	add_node( &head, 4);
	add_node( &head, 3);
	add_node( &head, 8);
	printf(" Linked Linked \n");
	// 2 → 9 → 1 → 5 → 6 → 4 → 3 → 8 → NULL
	display(head);
	find_sum_product(head);
	return 0;
}

Output

 Linked Linked
 2 → 9 → 1 → 5 → 6 → 4 → 3 → 8 → NULL
 Prime Sum     : 10
 Prime Product : 30