Inserting an element at the tail of linked list - c++

Question

I am new to data structures. I finally got the hang of adding new element at the beginning of linked list
but now there is another problem. I have watched so many YouTube videos yet the problem isn't solved. I am trying to add an element at the end of this linked list but when I do the first two elements disappear. Please help!
#include <iostream>
using namespace std;
class Node{
public:
int data;
Node *next;
Node(){
data = 0;
next = NULL;
}
};
Node* add_end(Node* a, int new_data){
Node* ptr, *temp;
ptr = a;
temp = new Node();
temp->data = new_data;
temp->next = NULL;
while(ptr->next != NULL) {
ptr = ptr->next;
}
ptr->next = temp;
return ptr;
}
void print(Node* a){
while(a != NULL){
cout << a->data << " ";
a = a->next;
}
}
int main(){
Node *head = NULL;
Node *second = NULL;
Node *third = NULL;
head = new Node();
second = new Node();
third = new Node();
head->data = 1;
head->next = second;
second->data = 2;
second->next = third;
third->data = 3;
third->next = NULL;
cout << "Before Adding:\n";
print(head);
head = add_end(head, 4);
cout << "\nAfter Adding: \n";
print(head);
return 0;
}

Answer 1

The function add_end should return the pointer to the head node.
Your current implementation returns the pointer to the second last node, which is calculated in the process of adding element.
You should return a instead of ptr from the function add_end.
Also you should return temp before the loop when ptr is NULL, or NULL will be dereferenced and it may lead to runtime error.