ERROR: Expression Must Be a Modifiable lvalue

[CSCImajor18]

I've written a linked list and once I got to the end, it states that my list variable has the above error (within title). Not sure on what is wrong.

HEADER FILE:

#ifndef DoublyLinkedList_h
#define DoublyLinkedList_h

//typedef struct Node;

struct Node
{
	int data;
	Node *next,*previous;
	Node (int a, Node *pre, Node *next) : data(a), previous(pre), next(next)
	{
		if(pre) previous -> next = this;
		if (next) next -> previous = this;
	}
};

class DoublyLinkedList
{
public: 
	DoublyLinkedList(int);
	DoublyLinkedList();
	~DoublyLinkedList();
	Node *head;
	int size;
	void addNodeBefore (int);
	void addNodeAfter (int);
	void addNodeBeforeData (int, Node*);
	void addNodeAfterData (int, Node*);
	//void out(bool);
	void setData (int);
	void setNext (Node*);
	void setPrevious (Node*);
	void deleteData (int, bool);
	bool empty();
	bool findData(int);
};
#endif 

.CPP FILE:

#include <iostream>
#include <string>
#include <iomanip> 
#include "DoublyLinkedList.h"
using namespace std;

DoublyLinkedList::DoublyLinkedList (int data)
{
	head = new Node (data, NULL, NULL);
	head ->next = head ->previous = head;
	size = 3;
}

DoublyLinkedList::DoublyLinkedList()
{
	Node *temp = this->head;
	Node *temp2;
	while (temp->previous)
		temp = temp ->previous;
	while(temp)
	{
		temp2 = temp ->next;
		delete temp;
		temp = temp2;
	}
	temp = temp2 = NULL;
}

bool DoublyLinkedList::empty()
{
	return (this ->size == 0);
}

void DoublyLinkedList ::addNodeBefore (int data)
{
	Node *next = head;
	Node *previous = head ->previous;

	Node *temp2 = new Node (data, previous, next);
	size++
}

void DoublyLinkedList::addNodeAfter(int data)
{
	Node *next = head ->next;
	Node *previous = head;

	Node *temp2 = new Node (data, previous, next);
	size++;
}

/*void DoublyLinkedList::out(bool directly)
{
	if (directly)
	{
		Node *temp = head;
		do 
		{
			cout<<temp ->data;
			temp = temp->next;
		}
		while (temp != head);
	}
	else
	{
		Node *temp = head;
		do
		{
			cout<<temp->data;
			temp = temp ->previous;
		}
		while (temp != head);
	}
	cout<<endl;
}*/

void DoublyLinkedList::setData( int Data)
{
	this ->head->data = Data;
}
void DoublyLinkedList::setPrevious(Node* Previous)
{
	this ->head->previous = Previous;
}
void DoublyLinkedList::setNext( Node* Next)
{
	this ->head->next = Next;
}

bool DoublyLinkedList::findData (int find)
{
	int counterStart = 0;
	Node *temp = head;
	while (temp ->next != head)
	{
		if (temp ->data == find)
			counterStart++;
		temp = temp->next;
	}

	if (counterStart > 0)
	{
		cout<<" ' "<<find<<" ' was found"<<counterStart<<" time(s)"<<endl;
		return true;
	}
	else
	{
		cout<<" ' "<<find<<" ' was not found"<<endl;
		return false;
	}
}

void DoublyLinkedList::deleteData(int find, bool everything)
{
	Node *temp = head;
	while (temp)
	{
		if (temp ->data == find)
		{
			cout<<"Removing "<<find<<endl;
			temp ->previous->next = temp ->next;
			temp ->next->previous = temp ->previous;
			if (false)
				return;
		}
		temp = temp ->next;
	}
}

TESTER FILE:

#include <iostream>
#include <string>
#include <iomanip> 
#include "DoublyLinkedList.h"

using namespace std;

int main ()
{
	int list [] = {1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31};

	DoublyLinkedList *list;
	Node *current;

	list = new DoublyLinkedList (list[0]);

	for (size_t i = 1; i < strlen(list); i++)
		list -> addNodeAfter (list[i]);


system ("pause");
	return 0;
}

[kulkarnisr]

I didn't go through the entire code, but see the line no 10 and 12 in tester file. You have used the same name.

[abhishekm71]

haven't gone through your code in detail but one error that stands out is

int list [] = {1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31};

DoublyLinkedList *list; // double declaration of same identifier?? 

[cire]

I've written a linked list and once I got to the end, it states that my list variable has the above error (within title).

Errors generally come with a line number indicating which line the error occurred on. It would be helpful if you supplied the full text of the error message including the line number.

[CSCImajor18]

Thank you @kulkarnisr and @abhishekm71 ! I've fixed line 12, which fixed lines 15 and half of 18 .

@Cire: It was an error mentioned when I hovered over the variable when it came to line 12. Sorry for not mentioning that

Once I fixed the 3 lines, line 17 and the latter part of 18 are still not happy. Line 17 error states " 'strlen' : cannot convert parameter 1 from 'int [16]' to 'const char ' "
And line 18 error reads as " IntelliSense: no suitable conversion function from "DoublyLinkedList" to "int" exist "

CORRECTED THE CODE AS SO:

int main ()
{
	int providedNumbers [] = {1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31};

	DoublyLinkedList *list;
	Node *current;

	list = new DoublyLinkedList (list[0]);

	for (size_t i = 1; i < strlen(list); i++)
		list -> addNodeAfter (list[i]);


system ("pause");
	return 0;
}

[coder777]

you need to change the use of the variable as well:

int main ()
{
	int providedNumbers [] = {1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31};

	DoublyLinkedList *list;
	Node *current;

	list = new DoublyLinkedList (providedNumbers[0]);

	for (size_t i = 1; i < sizeof(providedNumbers) / sizeof(*providedNumbers); i++) // NOTE: strlen doesn't make sense here!
		list -> addNodeAfter (providedNumbers[i]);


system ("pause");
	return 0;
}

[abhishekm71]

list = new DoublyLinkedList (list[0]); // what is list[0]? not defined.

for (size_t i = 1; i < strlen(list); i++)
  list -> addNodeAfter (list[i]);
// list is a linked list. strlen(list) is incorrect. You will have to keep a count of
// the number of elements in the list. Also, you cannot directly access a node in the
// list by list[i]. You will have to iterate through all the nodes.