c - I get into a endless loop in linked list -

i want find out intersect between 2 linked list sorted,but endless loop ,i know set wrong condition after while don't know how fix that. pls me.

#include<stdio.h> #include<stdlib.h> typedef struct node {     int data;     struct node *next; }list;  list *intersect(list *l1, list *l2) {     list *result;     list *l1pos, *l2pos, *resultpos;      l1pos = l1;     l2pos = l2;     result = (list *)malloc(sizeof(list));     resultpos = result;     while(l1pos != null && l2pos != null) {         //endless loop         if(l1pos->data < l2pos->data) {             l1pos = l1pos->next;         } else if(l1pos->data > l2pos->data) {             l2pos = l2pos->next;         } else {             resultpos->data = l1pos->data;             l1 = l1pos->next;             l2 = l2pos->next;             resultpos->next = (list *)malloc(sizeof(list));             resultpos = resultpos->next;         }     }      return result; } 

when find intersection, don't change values of l1pos , l2pos, loop keeps choosing final else statement forever.

if want end loop, use break or set 1 of mentioned variables null.

otherwise can set both nodes next node , let loop continue until end of list:

l1pos = l1pos->next; l2pos = l2pos->next; 

also allocation of result questionable, since node allocated before known if loop found result, return node contain uninitialized values, , final node in list result contain uninitialized values. instead of allocating in advance, allocate when find node, , set next pointer of new node null list terminated. in case nothing found, function return result, null (as initialized null before loop).