搜索二叉树的建立

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
using namespace std;

struct Nod
{
    int num;
    Nod *left;
    Nod *right;
    Nod()
    {
        num=0;
        left=right=NULL;
    }
};

template <class TYPE>
Nod* buildBinarySortTree(TYPE *a,int i,int size,Nod *head,Nod * &h)
{
    if(i>=size)
    {
        return head;
    }
    if(h==NULL)
    {
        h=new Nod;
        h->num=a[i];
        head=(head?head:h);
        buildBinarySortTree(a,i+1,size,head,head);
    }
    else
    {
        if(a[i]>h->num)
        {
            buildBinarySortTree(a,i,size,head,h->right);
        }
        else
        {
            buildBinarySortTree(a,i,size,head,h->left);
        }
    }
    return head;
}

void displayBinarySortTree(Nod *head)
{
    if(head)
    {
        displayBinarySortTree(head->left);
        cout<<head->num;
        displayBinarySortTree(head->right);
    }
}

void freeBinarySortTree(Nod *head)
{
    if(head)
    {
        freeBinarySortTree(head->left);
        freeBinarySortTree(head->right);
        delete head;
    }
}

int main()
{
    int n;
    while(cin>>n&&n)
    {
        int i;
        int *a=new int[n+1];
        for(i=0;i<n;i++)
        {
            cin>>a[i];
        }
        Nod *head=NULL;
        head=buildBinarySortTree(a,0,n,head,head);
        displayBinarySortTree(head);
        freeBinarySortTree(head);
        delete a;
    }
    return 0;
}

/*
5
4 7 3 2 1
*/