Program to maintain a linked list

/* Program to maintain a linked list */

#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 addatbeg ( struct node **, int ) ;
void addafter ( struct node *, int, int ) ;
void display ( struct node * ) ;
int count ( struct node * ) ;
void delete ( struct node **, int ) ;

void main( )
{
struct node *p ;
p = NULL ; /* empty linked list */

printf ( "\nNo. of elements in the Linked List = %d", count ( p ) ) ;
append ( &p, 14 ) ;
append ( &p, 30 ) ;
append ( &p, 25 ) ;
append ( &p, 42 ) ;
append ( &p, 17 ) ;

display ( p ) ;

addatbeg ( &p, 999 ) ;
addatbeg ( &p, 888 ) ;
addatbeg ( &p, 777 ) ;

display ( p ) ;

addafter ( p, 7, 0 ) ;
addafter ( p, 2, 1 ) ;
addafter ( p, 5, 99 ) ;

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

delete ( &p, 99 ) ;
delete ( &p, 1 ) ;
delete ( &p, 10 ) ;

display ( p ) ;
printf ( "\nNo. of elements in the Linked List = %d", count ( p ) ) ;
}

/* adds a node at the end of a linked list */
void append ( struct node **q, int num )
{
struct node *temp, *r ;

if ( *q == NULL ) /* if the list is empty, create first node */
{
temp = malloc ( sizeof ( struct node ) ) ;
temp -> data = num ;
temp -> link = NULL ;
*q = temp ;
}
else
{
temp = *q ;

/* go to last node */
while ( temp -> link != NULL )
temp = temp -> link ;

/* add node at the end */
r = malloc ( sizeof ( struct node ) ) ;
r -> data = num ;
r -> link = NULL ;
temp -> link = r ;
}
}

/* adds a new node at the beginning of the linked list */
void addatbeg ( struct node **q, int num )
{
struct node *temp ;

/* add new node */
temp = malloc ( sizeof ( struct node ) ) ;

temp -> data = num ;
temp -> link = *q ;
*q = temp ;
}

/* adds a new node after the specified number of nodes */
void addafter ( struct node *q, int loc, int num )
{
struct node *temp, *r ;
int i ;

temp = q ;
/* skip to desired portion */
for ( i = 0 ; i < loc ; i++ )
{
temp = temp -> link ;

/* if end of linked list is encountered */
if ( temp == NULL )
{
printf ( "\nThere are less than %d elements in list", loc ) ;
return ;
}
}

/* insert new node */
r = malloc ( sizeof ( struct node ) ) ;
r -> data = num ;
r -> link = temp -> link ;
temp -> link = r ;
}

/* 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 ;
}

/* deletes the specified node from the linked list */
void delete ( struct node **q, int num )
{
struct node *old, *temp ;

temp = *q ;

while ( temp != NULL )
{
if ( temp -> data == num )
{
/* if node to be deleted is the first node in the linked list */
if ( temp == *q )
*q = temp -> link ;

/* deletes the intermediate nodes in the linked list */
else
old -> link = temp -> link ;

/* free the memory occupied by the node */
free ( temp ) ;
return ;
}

/* traverse the linked list till the last node is reached */
else
{
old = temp ; /* old points to the previous node */
temp = temp -> link ; /* go to the next node */
}
}

printf ( "\nElement %d not found", num ) ;
}