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Linked List Functions Trouble

RvBVakama (9)
I am experiencing trouble trying to create a unit test for all the functions in my Linked List. Mainly I'm having trouble with my insert function that builds but just does not insert, and my First function which just returns the data in the first slot of my Linked List.

I am getting the following error for my code: newNodeCatch = myList.First();

Error C2440 'return': cannot convert from 'int' to 'ListNode<T> *' UnitTest

PS. My teacher helped to create the Linked List with me so I assume it is all correct code but I find it quite difficult to follow.

PPS. Thank you for any replies at all.

The Code:

//==========================================================================
// source.cpp
//==========================================================================

void TestLinkedList()
{
printf("\n====================================================\n");
printf(" LINKED LIST FUNCTIONS TEST");
printf("\n====================================================\n\n");

LinkedList<int> myList;

Iter<int> iter;

printf("\nCreating and populating a new LinkedList . . .\n");

myList.PushFront(6);
myList.PushFront(3);
myList.PushFront(1);

myList.PushBack(78);
myList.PushBack(12);
myList.PushBack(34);

printf("Testing operator overloads, peek at the code to see!\n");

cout << endl << "Current values are" << endl;

iter = myList.Begin(); //=

while (iter != myList.End()) // != ==
{
std::cout << iter.value() << std::endl; //value()
++iter; // --
}

ListNode<int>* newNode = new ListNode<int>;

newNode->data = 5;

myList.Insert(newNode);

//moving the iter back to the start
while (iter != myList.Begin()) // != ==
{
--iter; // --
}

cout << endl << "Current values are" << endl;
while (iter != myList.End()) // != ==
{
std::cout << iter.value() << std::endl; //value()
++iter; //++ --
}

ListNode<int>* newNodeCatch = new ListNode<int>;

newNodeCatch = myList.First();
}

int main()
{
TestLinkedList();

system("pause");
return 0;
}

//==========================================================================
// LinkedList.h
//==========================================================================

#pragma once
#include "ListNode.h"
#include <crtdbg.h>

template <typename T>
class Iter
{
ListNode<T>* current;

public:

//=
Iter& operator=(ListNode<T>* other)
{
//LinkedList<int> other1;
current = other;
return *this;
}

//!=
bool operator!=(ListNode<T>* other)
{
if (current != other)
return true;
else
return false;
}

//==
bool operator==(ListNode<T>* other)
{
if (current == other)
return true;
else
return false;
}

//->
T value()
{
return current->data;
}

//++
void operator++()
{
current = current->next;
}

//--
void operator--()
{
current = current->prev;
}
};

template <typename T>
class LinkedList
{
public:

LinkedList()
{
start = new ListNode<T>();
_ASSERT(start);
end = new ListNode<T>();
_ASSERT(end);

start->next = end;
end->prev = start;

start->prev = nullptr;
end->next = nullptr;
}

~LinkedList()
{
delete end;
delete start;
}

void PushFront(T data)
{
ListNode<T>* node = new ListNode<T>();
_ASSERT(node);
node->data = data;
node->next = start->next;
start->next->prev = node;
start->next = node;
node->prev = start;
}

void PushBack(T data)
{
ListNode<T>* node = new ListNode<T>();
_ASSERT(node);
node->data = data;
node->prev = end->prev;
end->prev->next = node;
end->prev = node;
node->next = end;
}

void Insert(ListNode<T>* node)
{
ListNode<T>* firstNode = node;
ListNode<T>* lastNode = node->next;
ListNode<T>* newNode = new ListNode<T>*;
//ListNode<T>* newNode = new ListNode<T>;
_ASSERT(newNode);

firstNode = newNode->prev;
lastNode = newNode->next;

//delete node;
}

ListNode<T>* Begin()
{
return start->next;
}

ListNode<T>* End()
{
return end;
}

ListNode<T>* First()
{
_ASSERT(start->next != end);
return start->next->data;
}

ListNode<T>* Last()
{
_ASSERT(end->prev != start);
return end->prev->data;
}

int Count()
{
int m_count = 0;

ListNode<T>* current = start->next;

while (current != end)
{
++current;
++m_count;
}

return m_count;
}

ListNode<T>* Delete(ListNode<T>* node)
{
ListNode<T>* prevNode = node->prev;
ListNode<T>* nextNode = node->next;

prevNode->next = nextNode;
nextNode->prev = prevNode;

delete node;

return nextNode;
}

void Erase(Iter<T> & target)
{
target.current = Delete(target.current);
}

void Remove(T value)
{
ListNode<T>* current = start->next;

while (current != end)
{
if (current.data == value)
{
current = Delete(current);
}

else
{
++current;
}
}
}

void PopBack()
{
_ASSERT(end->prev != start);
Delete(end->prev);
}

void PopFront()
{
_ASSERT(start->next != end);
Delete(start->next);
}

void Clear()
{
ListNode<T>* current = start->next;

while (current != end)
{
current = Delete(current);
++current;
}
}

private:
ListNode<T>* start;
ListNode<T>* end;
int m_Iterator;
};

//==========================================================================
// ListNode.h
//==========================================================================

#pragma once
#include "ListNode.h"

template <typename T>
class ListNode
{
public:
ListNode() {};
~ListNode() {};

T data;
ListNode* next;
ListNode* prev;
};
Peter87 (11175)
I am getting the following error for my code: newNodeCatch = myList.First();

Error C2440 'return': cannot convert from 'int' to 'ListNode<T> *' UnitTest

Should First() and Last() return a value or a pointer to a node? If you want them to return a value you need to change the return type of those two functions from ListNode<T>* to T, and change the code in TestLinkedList() so that you assign the return value of myList.First() to an int variable.
dhayden (5795)
My teacher helped to create the Linked List with me so I assume it is all correct code

Well there's your problem :).

Insert() doesn't seem to do anything.

After putting it all in one file (for my own convenience) and fixing the compiler errors, it seems to work. Note that I had to #define _ASSERT because my compiler doesn't support it.

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// #include "ListNode.h"

#define _ASSERT(a)

template < typename T > class ListNode {
  public:
    ListNode() {
    };
    ~ListNode() {
    };

    T data;
    ListNode *next;
    ListNode *prev;
};

//==========================================================================
// LinkedList.h
//==========================================================================

// #include "ListNode.h"
// #include <crtdbg.h>

template < typename T > class Iter {
    ListNode < T > *current;

  public:

//=
    Iter & operator=(ListNode < T > *other) {
//LinkedList<int> other1;
	current = other;
	return *this;
    }

//!=
    bool operator!=(ListNode < T > *other)
    {
	if (current != other)
	    return true;
	else
	    return false;
    }

//==
    bool operator==(ListNode < T > *other)
    {
	if (current == other)
	    return true;
	else
	    return false;
    }

//->
    T value()
    {
	return current->data;
    }

//++
    void operator++()
    {
	current = current->next;
    }

//--
    void operator--()
    {
	current = current->prev;
    }
};


template < typename T > class LinkedList {
public:

    LinkedList() {
	start = new ListNode < T > ();
	_ASSERT(start);
	end = new ListNode < T > ();
	_ASSERT(end);

	start->next = end;
	end->prev = start;

	start->prev = nullptr;
	end->next = nullptr;
    }

    ~LinkedList() {
	delete end;
	delete start;
    }

    void PushFront(T data)
    {
	ListNode < T > *node = new ListNode < T > ();
	_ASSERT(node);
	node->data = data;
	node->next = start->next;
	start->next->prev = node;
	start->next = node;
	node->prev = start;
    }

    void PushBack(T data)
    {
	ListNode < T > *node = new ListNode < T > ();
	_ASSERT(node);
	node->data = data;
	node->prev = end->prev;
	end->prev->next = node;
	end->prev = node;
	node->next = end;
    }

    void Insert(ListNode < T > *node)
    {
	ListNode < T > *firstNode = node;
	ListNode < T > *lastNode = node->next;
	// ListNode < T > *newNode = new ListNode < T >;
	ListNode<T>* newNode = new ListNode<T>;
	_ASSERT(newNode);

	firstNode = newNode->prev;
	lastNode = newNode->next;

//delete node;
    }

    ListNode < T > *Begin() {
	return start->next;
    }

    ListNode < T > *End() {
	return end;
    }

    ListNode < T > *First() {
	_ASSERT(start->next != end);
	// return start->next->data;   // dmh
	return start->next;
    }

    ListNode < T > *Last() {
	_ASSERT(end->prev != start);
	// return end->prev->data;  // dmh
	return end->prev;
    }

    int Count()
    {
	int m_count = 0;

	ListNode < T > *current = start->next;

	while (current != end) {
	    ++current;
	    ++m_count;
	}

	return m_count;
    }

    ListNode < T > *Delete(ListNode < T > *node) {
	ListNode < T > *prevNode = node->prev;
	ListNode < T > *nextNode = node->next;

	prevNode->next = nextNode;
	nextNode->prev = prevNode;

	delete node;

	return nextNode;
    }

    void Erase(Iter < T > &target)
    {
	target.current = Delete(target.current);
    }

    void Remove(T value)
    {
	ListNode < T > *current = start->next;

	while (current != end) {
	    if (current.data == value) {
		current = Delete(current);
	    }

	    else {
		++current;
	    }
	}
    }

    void PopBack()
    {
	_ASSERT(end->prev != start);
	Delete(end->prev);
    }

    void PopFront()
    {
	_ASSERT(start->next != end);
	Delete(start->next);
    }

    void Clear()
    {
	ListNode < T > *current = start->next;

	while (current != end) {
	    current = Delete(current);
	    ++current;
	}
    }

  private:
    ListNode < T > *start;
    ListNode < T > *end;
    int m_Iterator;
};

//==========================================================================
// source.cpp
//==========================================================================

#include <iostream>

using std::cout;
using std::cin;
using std::endl;

void
TestLinkedList()
{
    cout <<"\n====================================================\n";
    cout <<" LINKED LIST FUNCTIONS TEST";
    cout <<"\n====================================================\n\n";

    LinkedList < int >myList;

    Iter < int >iter;

    cout <<"\nCreating and populating a new LinkedList . . .\n";

    myList.PushFront(6);
    myList.PushFront(3);
    myList.PushFront(1);

    myList.PushBack(78);
    myList.PushBack(12);
    myList.PushBack(34);

    cout <<"Testing operator overloads, peek at the code to see!\n";

    cout << endl << "Current values are" << endl;

    iter = myList.Begin();			 //=

    while (iter != myList.End())		 // != ==
    {
	std::cout << iter.value() << std::endl;	 //value()
	++iter;					 // --
    }

    ListNode < int >*newNode = new ListNode < int >;

    newNode->data = 5;

    myList.Insert(newNode);

//moving the iter back to the start
    while (iter != myList.Begin())		 // != ==
    {
	--iter;					 // --
    }

    cout << endl << "Current values are" << endl;
    while (iter != myList.End())		 // != ==
    {
	std::cout << iter.value() << std::endl;	 //value()
	++iter;					 //++ --
    }

    ListNode < int >*newNodeCatch = new ListNode < int >;

    newNodeCatch = myList.First();
}

int
main()
{
    TestLinkedList();

    system("pause");
    return 0;
}

RvBVakama (9)
Sorry to say dhayden I just ran your edited code and It does not seem to work. The output is the same before the insert.

http://puu.sh/wsM3s/a361141e36.png
Thomas1965 (4571)
I modified the test function and it failed already at the 2. assertion.
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void TestLinkedList()
{
    cout <<"\n====================================================\n";
    cout <<" LINKED LIST FUNCTIONS TEST";
    cout <<"\n====================================================\n\n";

    LinkedList <int> myList;
    _ASSERT(myList.Count() == 0);

    myList.PushBack(1);
    _ASSERT(myList.Count() == 1);

    auto first = myList.First();
    _ASSERT(first != nullptr);
    _ASSERT(first->data == 1);
}


@dhayden
I think a better way to deal with the missing _ASSERT is:
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#ifndef _ASSERT
#define _ASSERT(cnd) assert(cnd)
#endif

In this way all the assertions will work.
dhayden (5795)
Here is fixed version of Insert():
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    void Insert(ListNode < T > *node)
    {
        node->next = start->next;
        start->next->prev = node;
        start->next = node;
        node->prev = start;
    }

I stole the code directly from PushFront, which now becomes:
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    void PushFront(T data)
    {
        ListNode < T > *node = new ListNode < T > ();
        _ASSERT(node);
        node->data = data;
        Insert(node);
    }
RvBVakama (9)
Yeah, I suppose that still matches the requirements. Guess the teachers can't mark me down for that but I do have the feeling I'm supposed to use the Iter class...
Thomas1965 (4571)
Still doesn't work.
_ASSERT(myList.Count() == 1); fails
RvBVakama (9)
Remove the asserts you don't need them. It's just a visual studio thing. They do not change the code at all.
Thomas1965 (4571)
Of course they don't change the code, they only show that's sth. wrong. They are universal, _ASSERT is VS but assert is standard C++.
Look at his code
First I create an empty list and list.Count() == 0 which is correct.
Then I add one value and the count is still 0, if this is not wrong what is it then ????
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LinkedList <int> myList;
  _ASSERT(myList.Count() == 0);

  myList.PushBack(1);
  _ASSERT(myList.Count() == 1);
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