Add 1 to number represented by the linked list.cpp

#include <bits/stdc++.h> 
using namespace std; 

class Node  
{  
    public: 
    int data;  
    Node* next;  
};  
Node *newNode(int data)  
{  
    Node *new_node = new Node;  
    new_node->data = data;  
    new_node->next = NULL;  
    return new_node;  
}  
Node *reverse(Node *head)  
{  
    Node * prev = NULL;  
    Node * current = head;  
    Node * next;  
    while (current != NULL)  
    {  
        next = current->next;  
        current->next = prev;  
        prev = current;  
        current = next;  
    }  
    return prev;  
}  
Node *addOneUtil(Node *head)  
{  Node* res = head;  
    Node *temp, *prev = NULL;  

    int carry = 1, sum;  

    while (head != NULL) //while both lists exist  
    {  sum = carry + head->data; 
       carry = (sum >= 10)? 1 : 0; 
       sum = sum % 10; 
       head->data = sum;
       temp = head;  
        head = head->next;  
   }
   Node* addOne(Node *head)  
{ 
   head = reverse(head);  
    head = addOneUtil(head);  
     return reverse(head);  
}  
void printList(Node *node)  
{  
    while (node != NULL)  
    {  
        cout << node->data;  
        node = node->next;  
    }  
    cout<<endl; 
}  
int main(void)  
{  
    Node *head = newNode(1);  
    head->next = newNode(9);  
    head->next->next = newNode(9);  
    head->next->next->next = newNode(9);  

    cout << "List is ";  
    printList(head);  

    head = addOne(head);  

    cout << "\nResultant list is ";  
    printList(head);  

    return 0;  
}  

//Input Format:
//Enter the value of the nodes of the linked list.

//Output Format:
//Add 1 to the number represented by the linked list.

//Sample Input Format:
//1->9->9->->9

//Sample Output Format:
//2000