#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 ;
}