二叉树的递归创建和遍历

/*
author:justinzhang
email:uestczhangchao@gmail.com
time:2012-8-20 15:52:27
des.:using non recursive method to traverse binary tree
*/
#include <iostream>
using namespace std;

template<typename T> class btree
{
public:
    T data;
    btree *lchild, *rchild;
};

/*    create binary tree, with one parameter.
    the binary tree is inputed through pre order,
    1
   2 3, is input as 1 2 -1 -1 3 -1 -1,(-1 represent nil node);
*/
btree<double> * create_btr(btree<double> **root)
{
    double data ;
    cin>>data;
    /* -1.0 represent the nil node */
    if(data == -1.0)
    {
        *root=NULL;
    }
    else
    {
        *root = new btree<double>();
        (*root)->data = data;
        (*root)->lchild = create_btr(&(*root)->lchild);
        (*root)->rchild = create_btr(&(*root)->rchild);
    }
    return *root;
}

/*create binary tree without parameter!*/
btree<double>* create_btr()
{
    double data;
    cin >> data;
    if(data == -1)
        return NULL; //return nill node
    else
    {
        btree<double> *T = new btree<double>;
        T->data = data;
        T->lchild = create_btr();
        T->rchild = create_btr();
        return T;
    }
}

void preorder(btree<double> *r)
{
    if(r==NULL)
        return;
    cout << r->data << endl;
    preorder(r->lchild);
    preorder(r->rchild);
}

void inorder(btree<double> *r)
{
    if(NULL==r)
        return;
    inorder(r->lchild);
    cout << r->data<<endl;
    inorder(r->rchild);
}
void postorder(btree<double> *r)
{
    if(NULL==r)
        return ;
    postorder(r->lchild);
    postorder(r->rchild);
    cout << r->data<<endl;
}


int main()
{
    btree<double> *root = NULL;
    create_btr(&root);
    //btree<double> *T = create_btr();
    preorder(root);
    inorder(root);
    postorder(root);
    //inorder(T);
    return 0;
}