Binary tree class implematation - c++

Question

I have the following code. It creates a binary tree class. The functions are insert(), pre_order(), post_order(), in_order(). But when I debug it I get zeros values. Also I insert 9 values but only have 7 zeros. Why I did wrong?
#include <iostream>
using namespace std;
//Begin the construction of the BINARY TREE
struct tree_node {
tree_node *left;
tree_node *right;
int data;
};
//Declaring the class
class bst {
tree_node *root; //creating the root of the binary tree
public:
bst() {
root = NULL; //intialize the default construction, set the root to NULL
}
int is_empty() { //check for empty graph
return (root == NULL);
}
//Manipulating the Binary Tree
void insert(int item);
void remove_it(int value); //difficult implementation
//Graph Traversal of Binary Tree
void in_order_trav();
void in_order(tree_node *);
void pre_order_trav();
void pre_order(tree_node *);
void post_order_trav();
void post_order(tree_node *);
};
void bst::insert(int item) {
tree_node *p = new tree_node;
tree_node *parent;
p->left = NULL;
p->right = NULL;
parent = NULL;
if (is_empty()) {
root = p;
}
else {
tree_node *ptr;
ptr = root;
while (ptr != NULL) {
parent = ptr;
if (item > ptr->data)
ptr = ptr->right;
else
ptr = ptr->left;
}
if (item < parent->data)
parent->left = p;
else
parent->right = p;
}
}
/*************In Order Traversal*****************************/
// Begin
void bst::in_order_trav() {
in_order(root);
}
void bst::in_order(tree_node *ptr) {
if (ptr!=NULL) {
in_order(ptr->left);
cout << " " << ptr->data << " ";
in_order(ptr->right);
}
}
// End
/***********************************************************/
/*************Pre Order Traversal*****************************/
// Begin
void bst::pre_order_trav() {
pre_order(root);
}
void bst::pre_order(tree_node *ptr) {
if (ptr!=NULL) {
cout << " " << ptr->data << " ";
pre_order(ptr->left);
pre_order(ptr->right);
}
}
// End
/***********************************************************/
/*************Post Order Traversal*****************************/
// Begin
void bst::post_order_trav() {
post_order(root);
}
void bst::post_order(tree_node *ptr) {
if(ptr!=NULL) {
post_order(ptr->left);
post_order(ptr->right);
cout << " " << ptr->data << " ";
}
}
// End
/***********************************************************/
int main() {
bst bin_tree; //create the Binary Tree
bin_tree.insert(20);
bin_tree.insert(30);
bin_tree.insert(52);
bin_tree.insert(254);
bin_tree.insert(2);
bin_tree.insert(24);
bin_tree.insert(25);
bin_tree.insert(42);
bin_tree.insert(59);
bin_tree.in_order_trav(); //in order traversal
bin_tree.pre_order_trav(); //pre order traversal
bin_tree.post_order_trav(); //post order traversal
}

Answer 1

The node value should be initialized(p->data = item) at function insert() as below
void bst::insert(int item) {
tree_node *p = new tree_node;
tree_node *parent;
p->left = NULL;
p->right = NULL;
p->data = item;
parent = NULL;
... ...
}

Answer 2

Ok the solution is silly! -.-
I forgot to add that line in insert routine!
p->data = item;