W3Schools Tryit Editor

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

struct Node {
  int data;
  struct Node *left;
  struct Node *right;
};

struct Node *createNode(int value) {
  struct Node *newNode = malloc(sizeof(struct Node));
  if (newNode == NULL) {
    printf("Memory allocation failed\n");
    exit(1);
  }
  newNode->data = value;
  newNode->left = NULL;
  newNode->right = NULL;
  return newNode;
}

struct Node *insert(struct Node *root, int value) {
  // Found an empty spot: put the new node here
  if (root == NULL) {
    return createNode(value);
  }
  if (value < root->data) {
    root->left = insert(root->left, value);   // Go left
  } else {
    root->right = insert(root->right, value); // Go right
  }
  return root;
}

void printInOrder(struct Node *root) {
  if (root == NULL) {
    return;
  }
  printInOrder(root->left);  // First, everything smaller
  printf("%d ", root->data); // Then this node
  printInOrder(root->right); // Then everything bigger
}

void freeTree(struct Node *root) {
  if (root == NULL) {
    return;
  }
  freeTree(root->left);
  freeTree(root->right);
  free(root);
}

int main() {
  struct Node *root = NULL;
  int values[] = {50, 70, 30, 80, 20, 60, 40};
  int length = sizeof(values) / sizeof(values[0]);

for (int i = 0; i < length; i++) {
    root = insert(root, values[i]);
  }

printInOrder(root);
  printf("\n");

freeTree(root);
  return 0;
}