Add two numbers represented by linked lists

#include<stdio.h> #include<stdlib.h> /* Linked list node */ struct Node {     int data;     struct Node* next; }; /* Function to create a new node with given data */ struct Node *newNode(int data) {     struct Node *new_node = (struct Node *) malloc(sizeof(struct Node));     new_node->data = data;     new_node->next = NULL;     return new_node; } /* Function to insert a node at the beginning of the Doubly Linked List */ void push(struct Node** head_ref, int new_data) {     /* allocate node */     struct 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 */ struct Node* addTwoLists (struct Node* first, struct Node* second) {     struct Node* res = NULL; // res is head node of the resultant list     struct Node *temp, *prev = NULL;     int carry = 0, sum;     while (first != NULL || second != NULL) //while both lists exist     {         // 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;         else // If this is not the first node then connect it to the rest.             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(struct Node *node) {     while(node != NULL)     {         printf("%d ", node->data);         node = node->next;     }     printf("\n"); } /* Driver program to test above function */ int main(void) {     struct Node* res = NULL;     struct Node* first = NULL;     struct 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);     printf("Second List is ");     printList(second);     // Add the two lists and see result     res = addTwoLists(first, second);     printf("Resultant list is ");     printList(res);    return 0; } ------------------------------------------------------------------------------------------ nt FindLength(Node* n) { // find the length of a given linked list. int ret = 0; while(n) { ret++; n = n->next; } return ret; } Node* Add(Node* list1, Node* list2) { // this function is called first int state = FindLength(list1) - FindLength(list2); // if state > 0, list1 is longer // if state < 0, list2 is longer // if state == 0, list1 and list2 is of same length int carry = 0; Node* ret = Add2(list1, list2, carry, state); // add the two lists if ( carry > 0 ) { // handle carry for the leftmost digit Node* temp = new Node(carry); temp->next = ret; ret = temp; } return ret; } Node* Add2(Node* p1, Node* p2, int& carry, int state) { // helper function if ( p1 == NULL && p2 == NULL ) // if both are NULL, we are at the end return NULL; Node* ret = new Node(0); // create new node to return if ( state > 0 ) { // p1 is still longer than p2 // only advance p1's pointer and decrease state ret->next = Add2(p1->next, p2, carry, state-1); ret->data = carry + p1->data; // just sum carry and p1's data } else if ( state < 0 ) { // p2 is still longer than p1 // only advance p2's pointer and increase state ret->next = Add2(p1, p2->next, carry, state+1); ret->data = carry + p2->data; // just sum carry and p2's data. } else { // p1 and p2 are of same length // advance both pointers, state should stay untouched from now on(0). ret->next = Add2(p1->next, p2->next, carry, 0); ret->data = carry + p1->data + p2->data; // sum carry and both digits } carry = ret->data / 10; // calculate new carry ret->data %= 10; // update the current data to be smaller than 10 return ret; // return the new node }