Linked List - Recursive

#include <stdio.h>
#include <stdlib.h>

typedef struct Node {
    int key;
    struct Node *next;
} Node;

Node *create_node(int key, Node *next=nullptr) {
    Node *ptr = (Node*)malloc(sizeof(Node));
    ptr->key = key;
    ptr->next = next;
    return ptr;
}

Node *push_front(Node *head, int key) {
    return create_node(key, head);
}

Node *push_back(Node *head, int key) {
    if (!head)
        return create_node(key);
    head->next = push_back(head->next, key);
    return head;
}

Node *insert_in_order(Node *head, int key) {
    if (!head)
        return create_node(key);
    if (head->key >= key)
        return create_node(key, head);
    head->next = insert_in_order(head->next, key);
    return head;
}

Node *find_key(Node *head, int key) {
    if (!head)
        return nullptr;
    if (head->key == key)
        return head;
    return find_key(head->next, key);
}

Node *delete_key(Node *head, int key) {
    if (!head)
        return nullptr;
    if (head->key == key) {
        Node *tmp = head->next;
        free(head);
        return tmp;
    } else {
        head->next = delete_key(head->next, key);
        return head;
    }
}

void print_list(Node *head) {
    if (!head)
        printf("NULL\n");
    else {
        printf("%d -> ", head->key);
        print_list(head->next);
    }
}

Node *free_list(Node *head) {
    if (head) {
        free_list(head->next);
        free(head);
    }
    return nullptr;
}

int main()
{
    Node *p = nullptr, *head = nullptr;
    head = insert_in_order(head, 10);
    head = insert_in_order(head, 20);
    head = insert_in_order(head, 30);
    print_list(head);
    p = find_key(head, 50);
    print_list(p);
    p = find_key(head, 30);
    print_list(p);
    p = find_key(head, 20);
    print_list(p);
    head = delete_key(head,50);
    head = delete_key(head,20);
    print_list(head);
    head = free_list(head);
    print_list(head);

    return 0;
}