BiTree* create(BiTree*& T)//BiTree* T => BiTree*& T 如果不改为引用，T的值将无法在递归调用
                          //中修改
{
    int ch;
    cout<<"输入结点的值"<<endl;
    cin>>ch;
    if(ch == 999)
    {
        T=NULL;
        cout<<"输入结束"<<endl;
    }
    else {
        T=new BiTree;
        cout<<"继续输入,输入999结束:"<<endl;
        T->data=ch;//生成根结点
        cout<<T->data<<"'s left:"<<endl;
        create(T->lchild);
        cout<<T->data<<"'s right:"<<endl;
        create(T->rchild);
        
    }//else
    return T;
}//create

void preorder(BiTree*T)//......递归先序遍历........
{
    if(T)
    {
        cout<<T->data<<" "; //为了显示清楚，添加了一个空格
        preorder(T->lchild);
        preorder(T->rchild);
    }
}//