Program to copy one linked list into another using recursion

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

/* structure containing a data part and link part */
struct node
{
int data ;
struct node *link ;
} ;

void append ( struct node **, int ) ;
void copy ( struct node *, struct node ** ) ;
void display ( struct node * ) ;

void main( )
{
struct node *first, *second ;
first = second = NULL ; /* empty linked lists */

append ( &first, 1 ) ;
append ( &first, 2 ) ;
append ( &first, 3 ) ;
append ( &first, 4 ) ;
append ( &first, 5 ) ;
append ( &first, 6 ) ;
append ( &first, 7 ) ;

clrscr( ) ;
display ( first ) ;

copy ( first, &second ) ;

display ( second ) ;
}

/* adds a node at the end of the 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 ;
}

/* copies a linked list into another */
void copy ( struct node *q, struct node **s )
{
if ( q != NULL )
{
*s = malloc ( sizeof ( struct node ) ) ;

( *s ) -> data = q -> data ;
( *s ) -> link = NULL ;

copy ( q -> link, &( ( *s ) -> link ) ) ;
}
}

/* displays the contents of the linked list */
void display ( struct node *q )
{
printf ( "\n" ) ;

/* traverse the entire linked list */
while ( q != NULL )
{
printf ( "%d ", q -> data ) ;
q = q -> link ;
}
}