concatenate one linked list at end of another

/* CH4PR8.C: Program to concatenate one linked list at end of another and
than to erase all nodes present in the linked list */

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

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

void append ( struct node **, int ) ;
void concat ( struct node **, struct node ** ) ;
void display ( struct node * ) ;
int count ( struct node * ) ;
struct node * erase ( 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 ) ;

clrscr( ) ;
printf ( "\nFirst List : " ) ;
display ( first ) ;
printf ( "\nNo. of elements in the first Linked List = %d",
count ( first ) ) ;

append ( &second, 5 ) ;
append ( &second, 6 ) ;
append ( &second, 7 ) ;
append ( &second, 8 ) ;

printf ( "\n\nSecond List : " ) ;
display ( second ) ;
printf ( "\nNo. of elements in the second Linked List = %d",
count ( second ) ) ;

/* the result obtained after concatenation is in the first list */
concat ( &first, &second ) ;

printf ( "\n\nConcatenated List : " ) ;
display ( first ) ;

printf ( "\n\nNo. of elements in Linked List before erasing = %d",
count ( first ) ) ;

first = erase ( first ) ;
printf ( "\nNo. of elements in Linked List after erasing = %d",
count ( first ) ) ;
}

/* 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 ;
}

/* concatenates two linked lists */
void concat ( struct node **p, struct node **q )
{
struct node *temp ;

/* if the first linked list is empty */
if ( *p == NULL )
*p = *q ;
else
{
/* if both linked lists are non-empty */
if ( *q != NULL )
{
temp = *p ; /* points to the starting of the first list */

/* traverse the entire first linked list */
while ( temp -> link != NULL )
temp = temp -> link ;

temp -> link = *q ; /* concatenate the second list after the
first */
}
}
}

/* 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 ;
}
}

/* counts the number of nodes present in the linked list */
int count ( struct node *q )
{
int c = 0 ;

/* traverse the entire linked list */
while ( q != NULL )
{
q = q -> link ;
c++ ;
}

return c ;
}

/* erases all the nodes from a linked list */
struct node * erase ( struct node *q )
{
struct node *temp ;

/* traverse till the end erasing each node */
while ( q != NULL )
{
temp = q ;
q = q -> link ;
free ( temp ) ; /* free the memory occupied by the node */
}

return NULL ;
}