假设 node 是 Node * 类型的指针，表示树的某个节点.然后 inorder(Node *)定义如下:

Say that node is a pointer of type Node* representing some node of your tree. Then inorder(Node*) is defined as follows:

void inorder(Node* node)
{
    if (!node) // end the recursion if node == nullptr
       return; 
    inorder(node->left);            // display the left subtree
    std::cout << node->info << " "; // display the current node
    inorder(node->right);           // display the right subtree
}