Add as linked List numbers

// C++ program to add two numbers 
// represented by linked list 
#include <bits/stdc++.h> 
using namespace std; 

/* Linked list node */
class Node { 
public: 
	int data; 
	Node* next; 
}; 

/* Function to create a 
new node with given data */
Node* newNode(int data) 
{ 
	Node* new_node = new Node(); 
	new_node->data = data; 
	new_node->next = NULL; 
	return new_node; 
} 

/* Function to insert a node at the 
beginning of the Singly Linked List */
void push(Node** head_ref, int new_data) 
{ 
	/* allocate node */
	Node* new_node = newNode(new_data); 

	/* link the old list off the new node */
	new_node->next = (*head_ref); 

	/* move the head to point to the new node */
	(*head_ref) = new_node; 
} 

/* Adds contents of two linked lists and 
return the head node of resultant list */
Node* addTwoLists(Node* first, Node* second) 
{ 

	// res is head node of the resultant list 
	Node* res = NULL; 
	Node *temp, *prev = NULL; 
	int carry = 0, sum; 

	// while both lists exist 
	while (first != NULL 
		|| second != NULL) { 
		// Calculate value of next 
		// digit in resultant list. 
		// The next digit is sum of 
		// following things 
		// (i) Carry 
		// (ii) Next digit of first 
		// list (if there is a next digit) 
		// (ii) Next digit of second 
		// list (if there is a next digit) 
		sum = carry + (first ? first->data : 0) 
			+ (second ? second->data : 0); 

		// update carry for next calulation 
		carry = (sum >= 10) ? 1 : 0; 

		// update sum if it is greater than 10 
		sum = sum % 10; 

		// Create a new node with sum as data 
		temp = newNode(sum); 

		// if this is the first node then 
		// set it as head of the resultant list 
		if (res == NULL) 
			res = temp; 

		// If this is not the first 
		// node then connect it to the rest. 
		else
			prev->next = temp; 

		// Set prev for next insertion 
		prev = temp; 

		// Move first and second 
		// pointers to next nodes 
		if (first) 
			first = first->next; 
		if (second) 
			second = second->next; 
	} 

	if (carry > 0) 
		temp->next = newNode(carry); 

	// return head of the resultant list 
	return res; 
} 

// A utility function to print a linked list 
void printList(Node* node) 
{ 
	while (node != NULL) { 
		cout << node->data << " "; 
		node = node->next; 
	} 
	cout << endl; 
} 

/* Driver code */
int main(void) 
{ 
	Node* res = NULL; 
	Node* first = NULL; 
	Node* second = NULL; 

	// create first list 7->5->9->4->6 
	push(&first, 6); 
	push(&first, 4); 
	push(&first, 9); 
	push(&first, 5); 
	push(&first, 7); 
	printf("First List is "); 
	printList(first); 

	// create second list 8->4 
	push(&second, 4); 
	push(&second, 8); 
	cout << "Second List is "; 
	printList(second); 

	// Add the two lists and see result 
	res = addTwoLists(first, second); 
	cout << "Resultant list is "; 
	printList(res); 

	return 0; 
} 

// This code is contributed by rathbhupendra