check BST cpp

// http://code2begin.blogspot.com
// program to check if a given binary tree is a Binary search tree or not

#include <iostream>
#include <queue>
#include <map>
#include <list>
#include <stack>

using namespace std;

// node class
class node{
public:
    int data;
    node* left;
    node* right;
};

// function that returns a pointer to new node
node* createNode(int element){
    node* temp = (node*) malloc(sizeof(node));
    temp->data = element;
    temp->left = NULL;
    temp->right = NULL;
    return temp;
}

// function to check if the given binary tree is a BST or not
bool check_BST(node* current){
    if(current == NULL){
        return true;
    }
    if (current->left != NULL && current->data < current->left->data){
        return false;
    }
    if (current->right != NULL && current->data > current->right->data){
        return false;
    }
    return (check_BST(current->left) && check_BST(current->right));
}
int main() {

    node* head = createNode(1);
    head->left = createNode(2);
    head->right = createNode(3);
    head->left->left = createNode(4);
    head->left->right = createNode(5);
    head->right->right = createNode(6);
    head->left->left->right = createNode(7);
    head->right->right->left = createNode(8);
    head->left->left->right->left = createNode(9);
    head->left->left->right->left->left = createNode(10);
    head->right->right->left->right = createNode(11);

    node* head2 = createNode(5);
    head2->left = createNode(2);
    head2->right = createNode(12);
    head2->left->left = createNode(-4);
    head2->left->right = createNode(3);
    head2->right->left = createNode(9);
    head2->right->right = createNode(21);
    head2->right->right->left = createNode(19);
    head2->right->right->right = createNode(25);

    node* head3 = createNode(1);
    head3->left = createNode(2);
    head3->right = createNode(3);
    head3->left->left = createNode(4);
    head3->left->right = createNode(5);
    head3->right->right = createNode(6);
    head3->left->left->right = createNode(7);
    head3->right->right->left = createNode(8);
    head3->left->left->right->left = createNode(9);
    head3->left->left->right->left->left = createNode(10);
    head3->right->right->left->right = createNode(11);

    // cout<<"SPIRAL Level wise traversal of the above binary tree is : "<<endl;
    cout<<"Binary Tree #1 is a Binary Search Tree : "<<check_BST(head)<<endl;
    cout<<"Binary Tree #2 is a Binary Search Tree : "<<check_BST(head2)<<endl;
    cout<<"Binary Tree #3 is a Binary Search Tree : "<<check_BST(head3)<<endl;
}