Header file Correct?

[TheFearful]

I am having trouble finding out if I did the header correctly

#include <iostream>
#ifndef TREE
#define TREE

// Node class
class Node 
{
    int key;
    Node* left;
    Node* right;
public:
    Node() 
    { 
        key=-1; 
        left = NULL; 
        right = NULL; 
    };
    void setKey(int aKey) { key = aKey; };
    void setLeft(Node* aLeft) { left = aLeft; };
    void setRight(Node* aRight) { right = aRight; };
    int Key() { return key; };
    Node* Left() { return left; };
    Node* Right() { return right; };
};

// Tree class
class Tree {
     Node* root;
public:
     Tree();
     ~Tree();
     Node* Root() { return root; };
     void addNode(int key);
     void inOrder(Node* n);
     void preOrder(Node* n);
     void postOrder(Node* n);
private:
     void addNode(int key, Node* leaf);
     void freeNode(Node* leaf);
};

#endif

Am I allowed to put an include statement there?

[Ancient Dragon]

Move the include statement down below to line 4, after the ifdef statement. Yes, you can put include statements in header files, it's done all the time.

[Kristian_2]

You can hide node constructor body withing tree.cpp file as well.
Accessor functions could be const.
int Key() const { return key; };
Node* Left() const { return left; };
Node* Right() const { return right; };

void setKey(int aKey) could be void setKey(const int& aKey).
Same with 2 addNode functions.
void addNode(const int& key);
void addNode(const int& key, Node* leaf);