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Question

I want to know this error why it is occupied!!!

class node 
{
public:
    int data ;
    node *left ;
    node *right ;
} ;

class tree
{
public:
    node * root ;

public:
    tree() 
    {
        root = NULL ;
    }
    node* Insert(node* root, int num) // 
    {
        if(root == NULL) // root is null
        {
            node * temp = new node() ;
            temp->left = NULL ;
            temp->right = NULL ;
            temp->data = num ;
            root = temp ;
        }
        else if ( num < root->data )
        {
            root->left = Insert(root->left, num ) ;
        }
        else if ( num > root->data)
        {
            root->right = Insert(root->right, num ) ;
        }
        return root ;
    }
} ;
void main()
{
    tree * Tree = new tree() ;
    Tree->Insert(Tree->root, 10) ;
    cout << temp->root->data ;
}

when I execute this code, than I expect that root's data is 10. but really, root is null. why is root null?

I don't know !!!!

please teach me!!!

Answer 1

root is never updated in your Insert method. The passed root to method is not same as the member variable.

Do like following :

Tree->root = Tree->Insert(Tree->root, 10) ;

or pass address of root or use this->root = everywhere inside the method.

Overall the design need to be revisited, I assume you want to play and learn

Also make sure you release the memory once you're done. Currently you have memory leaks, everywhere.