Print binary search tree in increasing order

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Given a binary search tree (aka an "ordered binary tree"), iterate over the nodes to print them out in increasing order. So the tree...
       4
      / \
     2   5
    / \
   1   3
Produces the output "1 2 3 4 5". This is known as an "inorder" traversal of the tree.
Hint: For each node, the strategy is: recur left, print the node data, recur right.

Here is code in c/cpp:

void printTree(struct node* node) {

/*
 Given a binary search tree, print out
 its data elements in increasing
 sorted order.
*/
void printTree(struct node* node) {
  if (node == NULL) return;   printTree(node->left);
  printf("%d ", node->data);
  printTree(node->right);
}