merge sorted ll c++

#include <iostream>
#include <stack>

using namespace std;

class node{

protected:
    int element;
    node* link;

public:
    //constructor that accepts only element
    node(int element) {
        this->element = element;
        this->link = NULL;
    }

    //constructor that accepts both link and element
    node(int element, node* link){
        this->element = element;
        this->link = link;
    }

    //method to update the element
    void updateData(int element){
        this->element = element;
    }

    //method to update or setup link
    void updateLink(node* link){
        this->link = link;
    }

    //method to get the element from the node
    int getElement(){
        return this->element;
    }

    //method to get the next node
    node* getNextNode(){
        return this->link;
    }
};

class Linkedlist {
public:
    node *head;

    //constructor for the Linked List class
    Linkedlist() {
        head = NULL;
    }

    //returns head node
    node *getHead() {
        return this->head;
    }

    // method to add a node at the end
    void insert(int element) {
        node *tempNode = new node(element);
        node *p = head;
        if (head == NULL) {
            head = tempNode;
            return;
        }
        else {
            while (p->getNextNode() != NULL) {
                p = p->getNextNode();
            }
            p->updateLink(tempNode);
            return;
        }
    }

    //method to display all the elements of the Linked List
    void display() {
        cout << "\n";
        node *tempNode = head;
        while (tempNode != NULL) {
            if (tempNode->getNextNode() != NULL)
                cout << tempNode->getElement() << " --> ";
            else
                cout << tempNode->getElement();

            tempNode = tempNode->getNextNode();
        }
        return;
    }
};

// merge 2 sorted linked lists
node* merge(node* head1, node* head2){
    node* head = NULL;
    node* current = NULL;
    node* curr1 = head1;
    node* curr2 = head2;

    while(curr1 != NULL && curr2 != NULL){
        if(curr1->getElement() > curr2->getElement()){
            if(head == NULL){
                head = curr2;
                current = head;
            }else{
                current->updateLink(curr2);
                current = current->getNextNode();
            }
            curr2 = curr2->getNextNode();
        }else{
            if(head == NULL){
                head = curr1;
                current = head;
            }else{
                current->updateLink(curr1);
                current = current->getNextNode();
            }
            curr1 = curr1->getNextNode();
        }
    }

    if(curr1 != NULL){
        current->updateLink(curr1);
        current = current->getNextNode();
    }

    if(curr2 != NULL){
        current->updateLink(curr2);
        current = current->getNextNode();
    }

    return head;
}

int main() {
    cout<<"Program to merge 2 Linked Lists";
    Linkedlist l1;
    l1.insert(1);
    l1.insert(3);
    l1.insert(5);
    l1.insert(7);
    l1.insert(8);
    l1.insert(9);
    l1.insert(11);
    l1.insert(13);

    cout<<"\nFirst Linked list is : ";
    l1.display();

    Linkedlist l2;
    l2.insert(2);
    l2.insert(4);
    l2.insert(5);
    l2.insert(6);
    l2.insert(9);
    l2.insert(8);

    cout<<"\nSecond Linked list is : ";
    l2.display();

    l1.head = merge(l1.getHead(), l2.getHead());

    cout<<"\nMerged Linked list is : ";
    l1.display();

    return 0;
}