Depth-First Search

We go move towards the Leaves of a Tree as fast as possible, from left to right.

Visit the current node before visiting any nodes inside the left or right subtrees.

void preOrder(Node node) {
  if (node != NULL) {
    printf("%d ", node->elem);
    preOrder(node->LC);
    preOrder(node->RC);
  }
}

Visit the current node after visiting all nodes of its left subtree - then visit the right subtree.

This is the preferred way as it orders elements in a balanced Binary Tree.

void inOrder(Node node) {
  if (node != NULL) {
    inOrder(node->LC);
    printf("%d ", node->elem);
    inOrder(node->RC);
  }
}

We visit the left & right subtrees before visiting the current node.

void postOrder(Node node) {
  if (node != NULL) {
    postOrder(node->LC);
    postOrder(node->RC);
    printf("%d ", node->elem);
  }
}

References