Struct node{
 node leftChild;
 node rightChild;
 int data;}

foo (node head)
    {
    std::cout << head.leftChild.data;
    }

/* This is a problem because of the recursive nature of the structure. leftChild also
contains a leftChild itself, which also contains a leftChild, etc. forever. */
struct node
{
    node leftChild; // how big is leftChild? infinitely large!
    node rightChild; // how big is rightChild? infinitely large!
    int data;
}

/* This is not a problem because the size of a pointer is always 4 bytes (assuming 32-
bit system). You can allocate room for the child nodes without recursively requiring an
infinite amount of memory. */
struct node
{
    node* leftChild; // how big is leftChild? 4 bytes (assuming 32-bit system)
    node* rightChild; // how big is rightChild? 4 bytes (assuming 32-bit system)
    int data;
}

void foo(node head)
{
    std::cout << head.leftChild->data; // assuming leftChild points to a valid object!
}