Question

I am making a program for singly linked lists using multiple files and classes.

I have to have a Node.h, LinkedList.h, Node.cpp, LinkedList.cpp, and a main.cpp

I was having other problems but now my printList() function just prints “List()” instead of “List(node 1, node2, etc…)”

Here is the code I have: (I can’t change the Node.h and LinkedList.h files)

Node.h:

//
//  Node.h
//  Linked Lists
//

#ifndef Linked_Lists_Node_h
#define Linked_Lists_Node_h

class Node
{
public:
    Node(int data);
    int data;
    Node *next;

};

#endif

LinkedList.h:

//
//  LinkedList.h
//  Linked Lists
//

#ifndef Linked_Lists_LinkedList_h
#define Linked_Lists_LinkedList_h

#include "Node.h"

class LinkedList
{
private:
    Node *head;

public:
    LinkedList();
    void addNode(int data);
    void removeNode(int data);
    bool searchNode(int data);
    void printList();

};

#endif

Node.cpp

//
//  Node.cpp
//  Linked Lists
//

#include <iostream>
#include <cstdlib>

#include "LinkedList.h"
#include "Node.h"

using namespace std;

Node::Node(int data) {};

LinkedList.cpp

//
//  LinkedList.cpp
//  Linked Lists
//

#include <iostream>
#include <cstdlib>

#include "LinkedList.h"
#include "Node.h"

using namespace std;

LinkedList::LinkedList()
{
    head = NULL;
}

void LinkedList::addNode(int data)
{
    Node *newNode;
    newNode->data = data;
    newNode->next = NULL;

    Node *tmp = head;

    if(tmp != NULL)
    {
        while(tmp->next != NULL)
        {
            tmp = tmp->next;
        }

        tmp->next = newNode;
    }
}

void LinkedList::removeNode(int data)
{
    Node *tmp = head;

    if(tmp == NULL)
    {
        cout << "No node removed" << endl;
        return;
    }

    if(tmp->next == NULL)
    {
        delete tmp;
        head = NULL;
    }
    else
    {
        Node *previous;

        do
        {
            if(tmp->data == data)
            {
                break;
            }
            previous = tmp;
            tmp = tmp->next;
        }
        while(tmp != NULL);

        previous->next = tmp->next;

        delete tmp;
    }
}

bool LinkedList::searchNode(int data)
{
    Node *tmp = head;

    while(tmp != NULL)
    {
        if(tmp->data == data)
        {
            cout << "Node found" << endl;
            return true;
        }
        tmp = tmp->next;
    }
    cout << "Node not found" << endl;
    return false;
}

void LinkedList::printList()
{
    Node *tmp = head;

    if(tmp == NULL)
    {
        cout << "List()" << endl;
        return;
    }

    if(tmp->next == NULL)
    {
        cout << "List(" << tmp->data << ")";
    }
    else
    {
        do 
        {
            cout << "List(" << tmp->data;
            cout << ", ";
            tmp = tmp->next;
        } 
        while (tmp != NULL);

        cout << ")" << endl;
    }
}

main.cpp

//
//  main.cpp
//  Linked Lists
//

#include <iostream>
#include <cstdlib>

#include "LinkedList.h"
#include "Node.h"
#include "LinkedList.cpp"

using namespace std;

int main ()
{
    LinkedList list;

    int data;
    int choice;

    while(1) 
    {
        cout << " Select:" << endl;
        cout << "1 to add a node" <<endl;
        cout << "2 to remove a node" << endl;
        cout << "3 to search for a node" << endl;
        cout << "4 to exit" << endl;
        cout << endl;

        cin >> choice;

        switch(choice)
        {
            case 1: //insertion
                cout << "Enter node: ";
                cin >> data;
                list.addNode(data); //add a node
                break;
            case 2: //deletion
                cout << "Enter node: ";
                cin >> data;
                list.removeNode(data); //remove a node
                break;
            case 3: //search
                cout << "Enter node: ";
                cin >> data;
                list.searchNode(data); //search for a node
                break;
            case 4:
                exit(0); //exit the program
                break;
            default: //default case
                cout << "Please enter a valid choice (1 - 4)!" << endl;
                break;
        }
    }
    return 0;
}

If you could help me figure out my problem I would greatly appreciate it.

Answer 1

Your problem is in main.cpp:

#include "LinkedList.cpp"

Remove this line, you only need to include the headers.

Including cpp files will cause them to be compiled again, causing the symbols to be defined twice, which results in your error.

BONUS:

You also have one more mistake in LinkedList.cpp

Node *newNode;
newNode->data = data;
newNode->next = NULL;

You need to initialize newNode before you use it, something like:

Node *newNode = new Node(data);
newNode->data = data;
newNode->next = NULL;