This program adds numbers represented by two linked lists

add_linked_lists.c

#include<stdlib.h>
#include<stdio.h>

typedef struct node{
        int data;
        struct node *next;
} Node;

/* This function is actually helper function which does all house keeping like 
calculating lengths of lists,calling recursive implementation, creating extra 
node for carry in MSD,and adding any remaining nodes left in longer list. */

/* result is pointer to pointer to the head of resulting node */ 
void add_list2(Node *L1, Node *L2, int *carry, Node  **result){

        int len1 = 0;
        int len2 = 0;
        int diff =0;

        Node * current  = L1;
        while(current){
                current = current->next;
                len1++;
        }
        current = L2;

        while(current){
                current = current->next;
                len2++;
        }

        if(len1 < len2){
                current = L1;
                L1 = L2;
                L2 = current;
        }
        diff  = abs(len1-len2);
        current = L1;

        while(diff--)
                current = current->next;

      /* Call the recursive implementation */
        add_list(current, L2, carry, result);

        diff  = abs(len1-len2);

       /* Add remaining nodes in longer list */
        add_remaining(L1, carry, result, diff);

        if(*carry){
                Node * temp = (Node *)malloc(sizeof(Node));
                temp->next =  (*result);
                *result = temp;

        }
        return;
}
void add_list(Node *L1, Node *L2, int *carry, Node **result){

        int sum;
        if(!L1)
                return;


        add_list(L1->next, L2->next, carry, result);

        /*We have reached the last node of both lists, add them */
        Node * temp = (Node *)malloc(sizeof(Node));
        sum = L1->data + L2->data + (*carry);
        
        // Store carry
        *carry = sum/10;
        
         sum = sum%10;

        temp->data = sum;
        /* Link pointers in resulting linked list */
        temp->next =  (*result);

        /* change the resulting pointer. */
        *result = temp;

        return;

}
void add_remaining(Node * L1, int *carry, Node **result, int diff){
        int sum =0;

        if(!L1 || diff == 0)
                return;

        add_remaining(L1->next, carry, result, diff-1);

        Node * temp = (Node *)malloc(sizeof(Node));
        sum = L1->data + (*carry);
        *carry = sum/10;
        sum = sum%10;

        temp->data = sum;
        temp->next =  (*result);
        *result = temp;

        return;

}
/* Addition of a node to linked list */
void push(Node **head, int value){
        if(*head == NULL){
                (*head) = (Node *)malloc(sizeof(Node));
                (*head)->data = value;
                (*head)->next = NULL;
        }
        else{
                Node * temp = (Node *)malloc(sizeof(Node));
                if(temp){
                        temp->data = value;
                        temp->next = (*head);
                        *head = temp;
                }
        }
}

/* Driver program to run above code */
int main(){
        Node * L1 = NULL;
        Node * L2 = NULL;
        Node * result = NULL;
        int carry = 0 ;
        /* creating list 1 */
        push(&L1,3);
        push(&L1,4);
        push(&L1,6);
        push(&L1,7);
        /* creating list 2 */
        push(&L2,8);
        push(&L2,9);
        push(&L2,7);
      
        add_list2(L1,L2, &carry, &result);   
        return 0;
}