int delete_doctor(void) {
        if (head == nullptr) {
            cout << "The list is empty\n";
            return 0;
        }
        cout << "Enter the ID of the doctor you want to delete:\n";
        int val;
        cin >> val;
        if (head->key == val) {
            if (head->next == nullptr) {
                delete(head);
                head = tail = nullptr;
                return 1;
            }
            doctor_node *temp = head;
            head = head->next;
            delete(temp);
            return 1;
        }
        else {
            doctor_node *current = head;
            doctor_node *prev = current;

            while ((current->key != val) && (current->next != nullptr)) {
                prev = current;
                current = current->next;
            }

            if ((current->key != val) && (current->next == nullptr)) {
                cout << "Doctor not found\n";
                return 0;
            }
            else if ((current->key == val) && (current->next == nullptr)) {
                tail = prev;
                prev->next = nullptr;
                delete(current);
                return 1;
            }
            else {
                prev->next = current->next;
                delete(current);
                return 1;
            }
        }
    }