Program to compare two linked lists using recursion

/* Program to compare two linked lists using recursion */

#include <stdio.h>
#include <conio.h>
#include <alloc.h>

struct node
{
int data ;
struct node *link ;
} ;

void append ( struct node **, int ) ;
int compare ( struct node *, struct node * ) ;

void 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 ) ;

clrscr( ) ;
if ( compare ( first, second ) )
printf ( "Both linked lists are EQUAL" ) ;
else
printf ( "Linked lists are DIFFERENT" ) ;
}

/* 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 = 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 = 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 ) ;
}