Trouble in traversing BST - c++

Question

I started learning about trees and tried writing the code for BST. Unfortunately i am having trouble displaying the tree datas. I am trying to implement Depth-first traversal. But have no idea how to implement it. Below is my code
#include<iostream>
using namespace std;
class node
{
public:
int data;
node *left,*right;
};
class btree
{
private:
node *root;
public:
btree(){root=NULL;}
void insert(int value)
{node *temp=new node;
if(root == NULL)
{
temp->right=NULL;
temp->data=value;
temp->left=NULL;
root=temp;
}
else
insertHelper(root, value);
}
void insertHelper(node* Node, int value)
{
if(value < Node->data)
{
if(Node->left == NULL)
{
Node->left=new node;
Node->left->data=value;
Node->left->left=NULL;
Node->left->right=NULL;
}
else
insertHelper(Node->left, value);
}
else
{
if(Node->right== NULL)
{
Node->right = new node;
Node->right->data=value;
Node->right->left=NULL;
Node->right->right=NULL;
}
else
insertHelper(Node->right, value);
}
}
void disp()
{node*tmp=root;
if(tmp==NULL)
cout<<"empty"<<endl;
else
{
cout<<tmp->data<<endl;
disphelper(tmp);
}
}
void disphelper(node *tmp)
{
if(tmp->left!=NULL)
{
cout<<tmp->left->data<<endl;
tmp=tmp->left;
disphelper(tmp);}
if(tmp->right!=NULL)
{
cout<<tmp->right->data<<endl;
tmp=tmp->right;
disphelper(tmp);
}
}
};
int main()
{
btree binarytree;
binarytree.disp();
binarytree.insert(10);
binarytree.insert(5);
binarytree.insert(30);
binarytree.disp();
}
the output is
empty
10
5
Can anyone please tell me why 30 is not displayed?

Answer 1

MODIFY your code to
void disphelper(node *tmp)
{
if(tmp == NULL)
return;
cout<<tmp->data<<endl; // print data for current node
if(tmp->left!=NULL) // traverse left branch
{
//cout<<tmp->left->data<<endl;
//tmp=tmp->left;
disphelper(tmp->left);}
if(tmp->right!=NULL) // traverse right branch
{
//cout<<tmp->right->data<<endl;
//tmp=tmp->right;
disphelper(tmp->right);
}
}
And it should work.
void disp()
{node*tmp=root;
if(tmp==NULL)
cout<<"empty"<<endl;
else
{
disphelper(tmp);
}
}

Answer 2

The reason you're not getting any output here is that in disphelper() you are first checking whether the left node is NULL and then changing it when you recurse into it. Same when you recurse into the right node.
void disphelper(node *tmp)
{
if(tmp->left!=NULL)
{
cout<<tmp->left->data<<endl;
//tmp=tmp->left; // Get rid of this.
disphelper(tmp->left); // Use this.
}
if(tmp->right!=NULL)
{
cout<<tmp->right->data<<endl;
//tmp=tmp->right; // Get rid of this
disphelper(tmp->right); // Use this.
}
}
Instead of changing the value of temp, which should be the same for both comparisons, just pass the left or right node in.
Two other things. Firstly, you're leaking memory like mad here: In your insert(), you create a new object every time, but only use it the first time, every other time it leaks. Your node class should be taking care of memory by having a destructor which deletes both nodes.
Secondly, before you post code, could you please take the trouble to format it so that the indentation is consistent? It's not the pain it use to be to do this - a lot of editors will do it for you or you can use the excellent Astyle. I know it's a small point but it's irritating for those who read your code - including, presumably the guy who's going to mark you homework! Thanks :-)