Sum of palindromic numbers in a linked list

// C Program
// Sum of palindromic numbers in a linked list
#include <stdio.h>
 //For malloc function
#include <stdlib.h>

//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 insert(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;
	printf("\n Linked List : ");
	//iterating linked list elements
	while (temp != NULL)
	{
		printf("  %d", temp->data);
		//visit to next node
		temp = temp->next;
	}
	printf("\n");
}
//Check that whether given number is palindrome or not
int is_palindrome(int num)
{
	if (num < 0)
	{
		//negative number is not a part of palindrome number
		return 0;
	}
	int result = 0;
	int x = num;
	//Reversing the given number digit
	while (x != 0)
	{
		result = (result *10) + (x % 10);
		x = x / 10;
	}
	//true, when reverse number is equal to given num
	return result == num;
}
//Calculate sum of all nodes that value is form of palindrome
void sum_of_palindrome(struct Node *head)
{
	//Display element of linked list 
	display(head);
	//Define resultant variable
	int result = 0;
	//Get first node
	struct Node *temp = head;
	printf(" Palindrome Nodes : [");
	//iterating linked list elements
	while (temp != NULL)
	{
		if (is_palindrome(temp->data) == 1)
		{
			printf("  %d", temp->data);
			result += temp->data;
		}
		//visit to next node
		temp = temp->next;
	}
	printf("  ]\n");
	//Display the calculated result
	printf(" Total Sum :  %d \n", result);
}
int main()
{
	struct Node *head = NULL;
	//Create linked list
	insert( &head, 21);
	insert( &head, 111);
	insert( &head, 212);
	insert( &head, 11);
	insert( &head, 112);
	insert( &head, 7);
	insert( &head, -121);
	insert( &head, 124);
	insert( &head, 121);
	sum_of_palindrome(head);
	return 0;
}

Output

 Linked List :   21  111  212  11  112  7  -121  124  121
 Palindrome Nodes : [  111  212  11  7  121  ]
 Total Sum :  462