Doubly Linked List in C

#include <stdio.h>
#include <conio.h>
#include <malloc.h>
#include <windows.h>
/* structure representing a node of the doubly linked list */
struct dnode
{
 struct dnode *prev ;
 int data ;
 struct dnode * next ;
} ;
void d_append ( struct dnode **, int ) ;
void d_addatbeg ( struct dnode **, int ) ;
void d_addafter ( struct dnode *, int , int ) ;
void d_display ( struct dnode * ) ;
int d_count ( struct dnode *  ) ;
void d_delete ( struct dnode **, int ) ;
int main( )
{
 struct dnode *p ;
 p = NULL ;  /* empty doubly linked list */
 d_append ( &p , 11 ) ;
 d_append ( &p , 2 ) ;
 d_append ( &p , 14 ) ;
 d_append ( &p , 17 ) ;
 d_append ( &p , 99 ) ;
 system ( "cls" ) ;
 d_display ( p ) ;
 printf ( "No. of elements in the DLL = %d\n\n", d_count ( p ) ) ;
 d_addatbeg ( &p, 33 ) ;
 d_addatbeg ( &p, 55 ) ;
 d_display ( p ) ;
 printf ( "No. of elements in the DLL = %d\n\n", d_count ( p ) ) ;
 d_addafter ( p, 4, 66 ) ;
 d_addafter ( p, 2, 96 ) ;
 d_display ( p ) ;
 printf ( "No. of elements in the DLL = %d\n\n", d_count ( p ) ) ;
 d_delete ( &p, 55 ) ;
 d_delete ( &p, 2 ) ;
 d_delete ( &p, 99 ) ;
 d_display ( p ) ;
 printf ( "No. of elements in the DLL = %d\n\n", d_count ( p ) ) ;
 return 0 ;
}
/* adds a new node at the end of the doubly linked list */
void d_append ( struct dnode **s, int num )
{
 struct dnode *r, *q = *s ;
 /* if the linked list is empty */
 if ( *s == NULL )
 {
  /*create a new node */
  *s = ( struct dnode * ) malloc ( sizeof ( struct dnode ) ) ;
  ( *s ) -> prev = NULL ;
  ( *s ) -> data = num ;
  ( *s ) -> next = NULL ;
 }
 else
 {
  /* traverse the linked list till the last node is reached */
  while ( q -> next != NULL )
   q = q -> next ;
  /* add a new node at the end */
  r = ( struct dnode * ) malloc ( sizeof ( struct dnode ) ) ;
  r -> data = num ;
  r -> next = NULL ;
  r -> prev = q ;
  q -> next = r ;
 }
}
/* adds a new node at the begining of the linked list */
void d_addatbeg ( struct dnode **s, int num )
{
 struct dnode *q ;
 /* create a new node */
 q = ( struct dnode * ) malloc ( sizeof ( struct dnode ) ) ;
 /* assign data and pointer to the new node */
 q -> prev = NULL ;
 q -> data = num ;
 q -> next = *s ;
 /* make new node the head node */
 ( *s ) -> prev = q ;
 *s = q ;
}
/* adds a new node after the specified number of nodes */
void d_addafter ( struct dnode *q, int loc, int num )
{
 struct dnode *temp ;
 int i ;
 /* skip to desired portion */
 for ( i = 0 ; i < loc ; i++ )
 {
  q = q -> next ;
  /* if end of linked list is encountered */
  if ( q == NULL )
  {
   printf ( "There are less than %d elements\n", loc );
   return ;
  }
 }
 /* insert new node */
 q = q -> prev ;
 temp = ( struct dnode * ) malloc ( sizeof ( struct dnode ) ) ;
 temp -> data = num ;
 temp -> prev = q ;
 temp -> next = q -> next ;
 temp -> next -> prev = temp ;
 q -> next = temp ;
}
/* displays the contents of the linked list */
void d_display ( struct dnode *q )
{
 /* traverse the entire linked list */
 while ( q != NULL )
 {
  printf ( "%2d\t", q -> data ) ;
  q = q -> next ;
 }
 printf ( "\n" ) ;
}
/* counts the number of nodes present in the linked list */
int d_count ( struct dnode * q )
{
 int c = 0 ;
 /* traverse the entire linked list */
 while ( q != NULL )
 {
  q = q -> next ;
  c++ ;
 }
 return c ;
}
/* deletes the specified node from the doubly linked list */
void d_delete ( struct dnode **s, int num )
{
 struct dnode *q = *s ;
 /* traverse the entire linked list */
 while ( q != NULL )
 {
  /* if node to be deleted is found */
  if ( q -> data == num )
  {
   /* if node to be deleted is the first node */
   if ( q == *s )
   {
    *s = ( *s ) -> next ;
    ( *s ) -> prev = NULL ;
   }
   else
   {
    /* if node to be deleted is the last node */
    if ( q -> next == NULL )
     q -> prev -> next = NULL ;
    else
    /* if node to be deleted is any intermediate node */
    {
     q -> prev -> next = q -> next ;
     q -> next -> prev = q -> prev ;
    }
    free ( q ) ;
   }
   return ;  /* return back after deletion */
  }
  q = q -> next ; /* go to next node */
 }
 printf ( "%d not found.\n", num ) ;
}