Compare two linked lists using recursion

C: 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 ) ;
}