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Help with Linked Lists

Help with Linked Lists, Using Linked List with class

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UofMCreed	4 Oct, 2008 - 02:58 PM Post #1
New D.I.C Head Joined: 4 Oct, 2008 Posts: 8 My Contributions	Im having a little trouble understanding how to code a linked list in C++ Code. I understand how the Linked List works, but i am having trouble writting it in code. I have a class and i have several member functions in the class. I am having a difficult time coding them. Im new to programming, i have just under a years experience, any help would be appreciated. I understand the concepts im having trouble thinking and making sence of how to code it. The preconditions and posts are there for each function. HELP ME PLZ!!! CODE //This is the implementation file for the class ListType #include <iostream> #include <cstddef> //to access NULL #include "ListType.h" typedef NodeType* NodePtr; typedef int ItemType; struct NodeType { ItemType item; NodePtr next; }; List::List() //Post: listPtr is set to NULL. { listPtr = NULL; } //*************************************************************** List::List(const List& otherList) //Copy-constructor for ListType { //FILL IN CODE } //************************************************************* //This one in particuallar im confused on bool List::IsThere(ItemType item) const //Post: If item is in the list IsThere is // True; False; otherwise. { //FILL IN CODE } //************************************************************* void List::Insert(ItemType item) //Pre: item is not already in the list. //Post: item is the first item in the list. { //FILL IN CODE } //************************************************************* void List::Delete(ItemType item) //Pre: item is in the list. //Post: item is no longer in the list. { //FILL IN THE CODE } //************************************************************* void List::Print() const //Post: Items in the list are printed to the screen. { //FILL IN THE CODE. } //************************************************************* int List::Length() const //Post: Number of items have been counted; result returned { //FILL IN CODE } //*************************************************************** List::~List() //Post: All the components are deleted. { //FILL IN CODE }
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Sadaiy	4 Oct, 2008 - 03:16 PM Post #2
New D.I.C Head Joined: 3 Oct, 2008 Posts: 35 Thanked 1 times My Contributions	there are a lot of tutorials on the net about linked list (some are on this site) they will give you the code of the implementation of most of the functions you have listed.
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JackOfAllTrades

4 Oct, 2008 - 03:25 PM

Post #3

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Your list class must maintain a pointer to the head node of the list.

cpp

//This one in particuallar im confused on
bool List::IsThere(ItemType item) const
//Post: If item is in the list IsThere is
//        True; False; otherwise.
{
    // Pseudocode:
    // 1. Create a local pointer, pointing to the head of the list; if head is NULL,  list is empty so return false.
    // 2. Start loop of your choice.
    // 3. Check the value of the pointer's item, compare to passed-in ItemType, if the same, return true.
    // 4. If the value of the pointer's next is NULL, return false, else set local pointer to value of next pointer and continue loop.
}

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Sadaiy

4 Oct, 2008 - 05:23 PM

Post #4

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Joined: 3 Oct, 2008
Posts: 35

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Ok , here is my very basic implementation of those functions you have asked for but note that i couldn't get the copy constructor to work right so I left it empty... Also note that instead of listitemtype i used int...

cpp


#include <iostream>
#include "list.h"

using namespace std;

list::list()
{
	head = NULL;
	tail = NULL;
}

list::list(const list& otherList)
{

}

void list::insert(int data)
{
	if(head == NULL)
	{
		current = new node;
		head = current;
		tail = current;
		current->prev = NULL;
		current->next = NULL;
		current->data = data;
	}
	else if(head != NULL)
	{
		current = new node;
		current->next = NULL;
		tail->next = current;
		current->prev = tail;
		tail = current;
		current->data = data;
	}
}

void list::print() const
{
	node *display;
	display = head;

	while(display != NULL)
	{
		cout << display->data << " ";
		display = display->next;		
	}
}

int list::length() const
{
	int Length = 0;
	
	node *loopPtr;
	loopPtr = head;

	while(loopPtr != NULL)
	{
		++Length;
		loopPtr = loopPtr->next;
	}

	return Length;
}

bool list::isThere(int data) const
{
	node *testPtr;
	testPtr = head;

	while(testPtr != NULL)
	{
		if(testPtr->data == data)
			return true;
		else
			testPtr = testPtr->next;
	}

	return false;	
}

void list::del(int data)
{
	node *delPtr;
	delPtr = head;

	while(delPtr != NULL)
	{
		if(delPtr->data == data)
			break;
		else
			delPtr = delPtr->next;
	}

	if(delPtr == head)
	{	
		head = delPtr->next;
		delPtr->next->prev = delPtr->prev;
	}
	else if(delPtr == tail)
	{
		tail = delPtr->prev;
		delPtr->prev->next = delPtr->next;
	}
	else if(delPtr != NULL)
	{
		delPtr->next->prev = delPtr->prev;
		delPtr->prev->next = delPtr->next;
	}
	else
	{
		cout << "That value you entered is not part of the list!" << endl;
	}
}

list::~list()
{
	node* clear = head;
	node* var = NULL;

	while(clear)
	{
		var = clear->next;
		delete clear;
		clear = var;
	}

	var = NULL;
	clear = NULL;
}