Binary Search Tree - Insertion/Preorder/Inorder/Postorder

#include <bits/stdc++.h>

using namespace std;

struct Node {
    int key;
    Node *left, *right;
};

// this function creates new node with number x and return the pointer to it
Node *createNode(int x)
{
    Node *newNode = new Node();
    newNode->key = x;
    newNode->left = NULL;
    newNode->right = NULL;
    return newNode;
}

// this function inserts node 'x' a tree rooted at 'root'
// it will return root of the tree after update
// so you must use it like this:
// vvvvvvvvvvvvvvvvv
// root = insert(root, x); -------- (*)
// ^^^^^^^^^^^^^^^^^
Node *insert(Node *root, int x)
{
    if (root == NULL) // if empty, build a new node and return
        return createNode(x);
    // if exists, go left or go right
    if (x < root->key) {
        root->left = insert(root->left, x);
        // ^ this matches (*) pattern
    } else {
        root->right = insert(root->right, x);
        // ^ this matches (*) pattern
    }
    // don't forget to return original root after finishing
    return root;
}

void preorder(Node *root)
{
    if (root == NULL) return;
    printf("%d ", root->key);
    preorder(root->left);
    preorder(root->right);
}

void postorder(Node *root)
{
    if (root == NULL) return;
    postorder(root->left);
    postorder(root->right);
    printf("%d ", root->key);
}

void inorder(Node *root)
{
    if (root == NULL) return;
    inorder(root->left);
    printf("%d ", root->key);
    inorder(root->right);
}

int main()
{
    Node *root = NULL;
    root = insert(root, 5);
    root = insert(root, 10);
    root = insert(root, 3);
    root = insert(root, 7);
    preorder(root);
    printf("\n");
    postorder(root);
    printf("\n");
    inorder(root);
    printf("\n");

    return 0;
}