C++ Binary Tree Traversal Inorder, Preorder and Postorder - c++

Question

I'm currently working on a C++ project and part of it is to traverse the binary tree using inorder, preorder, and postorder.
class TNode
{
public:
int val;
TNode() {}
TNode(int v) { val = v; }
TNode * left;
TNode * right;
TNode * parent;
};
class BTree
{
void print_pre_order(TNode *r);// print the node as you traverse according to the order.
void print_in_order();
void print_post_order();
}
BTree::BTree()
{
root = new TNode(1);
root->parent = 0;
root->left = new TNode(2);
root->right = new TNode(3);
root->left->left = new TNode(4);
root->left->right = new TNode (5);
root->right->left = new TNode(6);
}
void BTree::print_pre_order(TNode *r)
{
if (r == 0)
{
return;
}
cout << r->val;
print_pre_order(r->left);
print_pre_order(r->right);
}
int main()
{
BTree y;
y.print_pre_order(y.root);
return 0;
}
In my default constructor, I've initialized values for some nodes, but when I run the code, the output I'm getting is "124" and gets an error. I don't know where I did wrong, can someone help?

Answer 1

I see no signs that the program ever sets any any pointers to zero, so if (r == 0) is unlikely to ever trigger an exit.
Give this a try:
class TNode
{
public:
int val;
TNode(): val(0), left(nullptr), right(nullptr), parent(nullptr) {}
TNode(int v): val(v), left(nullptr), right(nullptr), parent(nullptr) {}
TNode * left;
TNode * right;
TNode * parent;
};
The : tells the compiler that a member initializer list is coming. After that the code initializes all of the pointer members to point at null.
Change the
if (r == 0)
to
if (r == nullptr)
to better convey intent and you should be good to go.