Doubly Circular Linked List - Insertion - based on user input.cpp

#include <iostream>
using namespace std;

struct NODE {
    int data;
    NODE *prev;
    NODE *next;
};

NODE *head, *tail, *prevnode;
void add(int value){
    if(head == NULL){
        head = tail = new NODE;
        head->data = value;
        head->prev = head->next = tail;
    } else {
        prevnode = tail;
        tail->next = head->prev = new NODE;
        tail = tail->next;
        tail->prev = prevnode;
        tail->data = value;
        tail->next = head;
    }
}

int print(NODE *ref){
    if(ref == 0){
        cout << "[EMPTY LIST]" << endl;
        return false;
    } else {
        do {
            cout << ref->data;
            ref = ref->next;
            if(ref != head) cout << " => ";
        } while(ref != head);
        cout << endl;
        return true;
    }
}

int main(){
    cout << "Note! Enter zero (0) to exit from entering input. " << endl;
    int input = 1, i = 0;
    while(input != 0){
        cout << "Enter a value for the NODE-" << ++i << ": ";
        cin >> input;
        if(input != 0) add(input);
    }
    cout << endl << "Linked List: ";
    print(head);
}