Adding a node to the end of a linked list

Question

I've been trying to add an item to the end of a linked list. I think I have a handle on the concept but i'm having difficulty implementing the code. In particular, being able to traverse a linked list and find the tail. Here is what i have so far. I've been at this for a while trying different things. Any help would be appreciated.

##include <iostream>
using namespace std;


class node
{
public:
    int data;
    node *next;
};


class linkedList
{
private:
    node* ptrHead;
    node* ptrTail;

    int size;

public:
    linkedList();  //default constructor
    void display();
    void addFront(int);
    void removeFront();
    void addBack(int);
    void removeBack();
};

//default constructor
linkedList::linkedList(){
    size = 0;
    ptrHead = ptrTail = NULL;
}
//display linked list
void linkedList::display(){
    node* current = ptrHead;

    while (current != NULL) {
        cout << current->data << " "; //display current item
        current = current->next; //move to next item
    }
    cout << size;
}
//add item to front of linked list
void linkedList::addFront(int addData){

    node* n = new node;
    n->next = ptrHead;
    n->data = addData;
    ptrHead = n;

    size++;
}
//remove item from front of linked list
void linkedList::removeFront(){

    node* n = ptrHead;
    ptrHead = ptrHead->next;
    delete n;

    size--;
}

       void linkedList::addBack(int addData){   ////work in progress


        node* n = new node; //create new node
        n->data = addData;  //input data
        n->next = NULL;     //set node to point to NULL

        if ( ptrTail == NULL )  // or if ( ptrTail == nullptr )
        {
            ptrHead = n;
            ptrTail = n;
        }
        else
        {
            ptrTail->next = n;
            ptrTail = n;
        }

        size++;
    }



    //this is the test code from my main function
              int main()
        {
            //test code
            linkedList list;

            list.addFront(40);
            list.addFront(30);
            list.addFront(20);
            list.addFront(10);
            list.addFront(0);
            list.addBack(50);
            list.addBack(60);

            list.display(); //50 60 7  (the 7 is the count/size of the linked list)
            cout << endl;
        }

Answer 1

You did not show the definition of your linkedList.

So I can only suppose that it has data members ptrTail and ptrHead. In this case the function will look the following way

void linkedList::addBack(int addData)
{
   node* n = new node; //create new node
   n->data = addData;  //input data
   n->next = NULL;     //set node to point to NULL

   if ( ptrTail == NULL )  // or if ( ptrTail == nullptr )
   {
      ptrHead = n;
   }
   else
   {
      ptrTail->next = n;
   }
   ptrTail = n;

   size++;
}

Function addFront can be defined the similar way

void linkedList::addFront(int addData)
{
   node* n = new node; //create new node
   n->data = addData;  //input data

   if ( ptrHead == NULL )  // or if ( ptrHead == nullptr )
   {
      ptrTail = n;
   }

   n->next = ptrHead;
   ptrHead = n;

   size++;
}

One more function

void linkedList::removeFront()
{
    if ( ptrHead != NULL )
    {
        if ( ptrTail == ptrHead ) ptrTail = NULL;
        node* n = ptrHead;
        ptrHead = ptrHead->next;
        delete n;
        size--;
    }
}

Answer 2

for(int i=1; i<size; i++)
   pCurrent = pCurrent->next;

pCurrent = n;

This will work. But you have to keep the size variable as real size of the Linked List.

Or If you want to add element in the end always, you can follows the below steps. Keep a extra node tail and add the element to that.

if(head == NULL)
{
   head = n;
   tail = n;
}
else
{
   tail->next = n;
   tail = tail->next;
}

Answer 3

Try this

node* pCurrent = ptrHead;
if( pCurrent != NULL ){
    //find tail
    while (pCurrent->next != NULL)
        pCurrent = pCurrent->next;

    // add new node at end of tail
    pCurrent->next = n;
    } else {
        pCurrent = n;
    }
}