Simple Double Linked List Implementation in C++

linkedlist_d.cpp

#include <iostream>
using namespace std;
#define null 0

class Node {
    public:
        int data;
        Node *next;
        Node *prev;
        Node(int data) {
            this->data = data;
            next = NULL;
            prev = NULL;
        }
};

class LinkedList {
    private:
        Node *header;
        Node *tail;
        int size;
        
    public:
        LinkedList() {
            header = NULL;
            tail = NULL;
            size = 0;
        }
        
        int getSize() {
            return size;
        }
        
        void append(int data) {
            Node *n = new Node(data);
            if(header == null) {
                header = n;
                tail = n;
            } else {
                tail->next = n;
                n->prev = tail;
                tail = n;
            }
            size++;
        }
        
        void prepend(int data) {
            Node *n = new Node(data);
            if(header == null) {
                header = n;
                tail = n;
            } else {
                header->prev = n;
                n->next = header;
                header = n;
            }
            size++;
        }
        
        void insertAt(int pos, int data) {
            if(pos > size + 1 || pos < 1) return;
            else if(pos == 1) prepend(data);
            else if(pos == size + 1) append(data);
            else if(header != null) {
                Node *n = new Node(data);
                Node *current = header;
                for(int i = 1; i < pos; i++) current = current->next;
                current->prev->next = n;
                n->prev = current->prev;
                n->next = current;
                current->prev = n;
                size++;
            }
        }
        
        void removeHeader() {
            if(header->next == null) {
                delete(header);
                header = null;
                tail = null;
            } else if(header != null) {
                header = header->next;
                delete(header->prev);
                header->prev = null;
            }
            size--;
        }
        
        void removeTail() {
            if(header->next == null) removeHeader();
            else if(header != null) {
                tail = tail->prev;
                delete(tail->next);
                tail->next = null;
                size--;
            }
        }
        
        void removeAt(int pos) {
            if(pos > size || pos < 1) return;
            else if(pos == 1) removeHeader();
            else if(pos == size) removeTail();
            else if(header != null) {
                Node *current = header;
                for(int i = 1; i < pos; i++) current = current->next;
                current->prev->next = current->next;
                current->next->prev = current->prev;
                delete(current);
                size--;
            }
        }
                
        void print() {
            Node *temp = header;
            while(temp != NULL) {
                cout << temp->data << endl;
                temp = temp->next;
            }
            cout << endl;
        }
        
        void printReverse() {
            Node *n = tail;
            while(n != null) {
                cout << n->data << endl;
                n = n->prev;
            }
            cout << endl;
        }
        
        void test() {
            prepend(3);
            prepend(1);
            prepend(5);
            print();
            append(8);
            append(7);
            print();
            insertAt(2, 9);
            insertAt(4, 11);
            print();
            printReverse();
            removeHeader();
            print();
            removeAt(3);
            print();
            removeTail();
            print();
        }
                
        ~LinkedList() {
            Node *next = header->next;
            while(header != null) {
                next = header->next;
                delete(header);
                header = next;
            }
        }
};

int main() {
    LinkedList list;
    list.test();
    //system("pause");
    return 0;
}