Linked list in c++ adding node at the end of the list

I am writing a code which will store elements in linked list, however when i'm adding an element at the end of the list the output is always like this...

enter image description here
i've already search from many tutorials and copying their code to see if it works on mine but it doesn't..

#include <iostream>
#define tab '\t'

using std::endl;

struct node {
    int data;
    node* next;
};

class Linkedlist {
private:
    node* head = new node;

public:
    Linkedlist(){
        head->next = NULL;
    }

    void addStart(int val){
        node* temp = new node;
        temp->data = val;
        temp->next = head;
        head = temp;
    } 
    
    void addEnd(int val){
        node* temp = new node;
        temp->data = val;
        temp->next = NULL;

        node* curr = new node;
        curr = head;
        while(curr->next != NULL){
            curr = curr->next;
        }
        curr->next = temp;
    } 

    void display(){
        if (head == NULL){
            std::cout << endl << "Linked List is EMPTY.";
        } else {
            int i = 1;
            node* curr = new node;
            curr = head;

            std::cout << endl << "The linked list contains..." << endl;
            while(curr->next != NULL){
                std::cout << "Elements " << i << ':' 
                    << tab << curr->data << endl;
                curr = curr->next;
                i++;
            }
        }
    }
};

The Output should be..
Element 1: 1
Element 2: 2
Element 3: 3
Element 4: 4

If you use addEnd on an empty list, head will point to NULL. Then, when you do curr = head, curr is also NULL. Then, you do while (curr->next != NULL), which is illegal since curr is NULL, so curr->next points to unknown memory.

You can add a condition checking if head is NULL:

void addEnd(int val) {
    if (head == NULL) {
        this->addStart(val);
        return;
    }
    //the rest of the code
}

The above code checks if head is NULL. If it is, the list is empty, and adding an element to the end of the list is functionally equivalent to adding an element to its start. You can just use addStart in that case.

Bugs:

1. at addStart() function:

> temp->next = head;
> head = temp;

Problem: This code never kept the last nodes' next as NULL
Solution:
a) declared head as null
b) writing code for 2 different conditions (when the head is NULL and not NULL):

 Linkedlist(){
        head= NULL;
    }

    void addStart(int val){
        node* temp = new node;
        temp->data = val;
        
        if(head == NULL){
            head = temp;
            head->next = NULL;
            return;
        }  else {
            temp->next = head;
            head = temp;
            return;
        }

           }

2. You didn't display the last node.
   Soln: change while loop condition in display function from

> curr->next != NULL

to

> curr != NULL.

OVERALL CODE:

  #include <iostream>
    #define tab '\t'
    
    using std::endl;
    
    struct node {
        int data;
        node* next;
    };
    
    class Linkedlist {
    private:
        node* head = new node ;
        
       
    
    public:
        Linkedlist(){
            head= NULL;
        }
    
        void addStart(int val){
            node* temp = new node;
            temp->data = val;
            
            if(head == NULL){
                head = temp;
                head->next = NULL;
                return;
            }  else {
                temp->next = head;
                head = temp;
                return;
            }
    
               } 
        
        void addEnd(int val){
            node* temp = new node;
            temp->data = val;
            temp->next = NULL;
    
           node* curr = new node;
            curr = head;
    
           
            while(curr->next != NULL){
                curr = curr->next;
             
            }
            curr->next = temp;
           
        } 
    
        void display(){
            if (head == NULL){
                std::cout << endl << "Linked List is EMPTY.";
            } else {
                int i = 1;
                node* curr = new node;
                curr = head;
    
                std::cout << endl << "The linked list contains..." << endl;
                while(curr != NULL){
                    std::cout << "Elements " << i << ':' 
                        << tab << curr->data << endl;
                    curr = curr->next;
                    i++;
                }
            }
        }
    };