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…)”

I think my insert might be the problem because my searchNode() doesn’t work right either, it always says node not found.

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;
    }
    cout << "Node added" << endl;
    printList();
}

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;
    }
    cout << "Node removed" << endl;
    printList();
}

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

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

You’re not adding any nodes. If head is NULL, your add Node becomes:

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

    Node *tmp = head;

    if(tmp != NULL)
    { 
        //this never gets executed
    }
    cout << "Node added" << endl;
    printList();
}

You need to treat this case (first insertion):

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;
    }
    else
    {
        head = newNode;
    }
    cout << "Node added" << endl;
    printList();
}

This will create the head if it doesn’t exist already.

Are you using a debugger? It would be much easier (for you) if you did.