//------------------- list2.cpp -------------------------
//------------ source file for unit list ----------------

#include <stdio.h>
#include <stdlib.h>
#include <conio.h>
#include "list2.h"

//--------------------------- Iplementstion -----------------------------

//---------------------------------------------------------------
//              returns an initialized list
list_type list_init (void)
{
	list_type L;
	L.anchor = (pos_type) malloc (sizeof(struct link_type));
	L.anchor->next = NULL;
	return L;
}

//---------------------------------------------------------------
//  	   return  place:  anchor
//    assumption: L is initialized
pos_type list_anchor (list_type L)
{
	return L.anchor;
}

//---------------------------------------------------------------
//  	   return  place:  list_end
//    assumption: L is initialized
pos_type list_end (list_type L)
{
	return NULL;
}

//---------------------------------------------------------------
//  	   return  place:  next link in list
//    assumption: L is initialized
pos_type list_next (list_type L, pos_type pos)
{
	return (pos->next);
}

//---------------------------------------------------------------
//  	   return  place:  previous link in list
//    assumption: L is initialized
pos_type list_prev (list_type L, pos_type pos)
{
	pos_type p;

	p = list_anchor(L);
	while (list_next (L,p) != pos)
		p = list_next (L,p);
	return p;
}

//---------------------------------------------------------------
//  	inserting x after pos in L
//    assumption: L is initialized
void list_insert (list_type &L, pos_type pos, list_info_type x)
{
	pos_type temp;

	temp = (pos_type) malloc (sizeof (struct link_type));
	temp->info = x;
	temp->next = pos->next;
	pos->next  = temp;
}

//---------------------------------------------------------------
//  	delets link in place pos in L
//      after deletation, pos points to next item before deletation
//    assumption: L is initialized, pos points to place in list
//			     which is neither anchor nor list-end.
void list_delete (list_type &L, pos_type &pos)
{
	pos_type temp;

	temp = list_prev (L,pos);
	temp->next = pos->next;
	free (pos);
	pos = temp->next;
}

//---------------------------------------------------------------
//  	   returns data from place pos in L
//    assumption: L is initialized, pos points to place in list
//			     which is neither anchor nor list-end.
list_info_type list_retrieve (list_type L, pos_type pos)
{
	return pos->info;
}

//---------------------------------------------------------------
//  	return TRUE if list is empty, atherwise return FALSE
//    assumption: L is initialized
int list_is_empty (list_type L)
{
	return L.anchor->next == NULL;
}

//---------------------------------------------------------------
//  	   updats data in place pos in L
//    assumption: L is initialized, pos points to place in list
//			     which is neither anchor nor list-end.
void list_update (list_type &L, pos_type pos, list_info_type x)
{
	pos->info = x;
}