Comparing 2 Linked Lists through Recursion in C

#include <stdio.h>
#include <conio.h>
#include <malloc.h>
#include <windows.h>
struct node
{
 int data ;
 struct node *link ;
} ;
void append ( struct node **, int ) ;
int compare ( struct node *, struct node * ) ;
int main( )
{
 struct node *first, *second ;
 first = second = NULL ;  /* empty linked lists */
 append ( &first, 1 ) ;
 append ( &first, 2 ) ;
 append ( &first, 3 ) ;
 append ( &second, 1 ) ;
 append ( &second, 2 ) ;
 append ( &second, 3 ) ;
 system ( "cls" ) ;
 if ( compare ( first, second ) )
  printf ( "Both linked lists are EQUAL\n" ) ;
 else
  printf ( "Linked lists are DIFFERENT\n" ) ;
 return 0 ;
}
/* adds a node at the end of a linked list */
void append ( struct node **q, int num )
{
 struct node *temp ;
 temp = *q ;
 if ( *q == NULL )  /* if the list is empty, create first node */
 {
  *q = ( struct node * ) malloc ( sizeof ( struct node ) ) ;
  temp = *q ;
 }
 else
 {
  /* go to last node */
  while ( temp -> link != NULL )
   temp = temp -> link ;
  /* add node at the end */
  temp -> link = ( struct node * ) malloc ( sizeof ( struct node ) ) ;
  temp = temp -> link ;
 }
 /* assign data to the last node */
 temp -> data = num ;
 temp -> link = NULL ;
}
/* compares 2 linked lists and returns 1 if linked lists are equal and 0 if
 unequal */
int compare ( struct node *q, struct node *r )
{
 static int flag ;
 if ( ( q == NULL ) && ( r == NULL ) )
  flag = 1 ;
 else
 {
  if ( q == NULL || r == NULL )
   flag = 0 ;
  if ( q -> data != r -> data )
   flag = 0 ;
  else
   compare ( q -> link, r -> link ) ;
 }
 return ( flag ) ;
}