先序遍历：

struct node{
  int data;
  node *lchild,*rchild;
};

void PreOrder(node *T)
{
    node *p = T;
    Stack s;

    while(p || isempty(s))
    {
        while(p)
        {
            push(p);
            printf("%d",p->data);
            p = p->lchild;
        }

        if(!isempty(s))
        {
            p = pop(s);
            p = p->rchild;
        }
    }
}

中序遍历：

struct node{
  int data;
  node *lchild,*rchild;
};

void InOrder(node *T)
{
    node *p = T;
    Stack s;
    while(p || !isempty(s))
    {
        while(p)
        {
            push(p);
            p = p->lchild;
        }

        if(isempty(s))
        {
            p = pop(s);
            printf("%d",p->data);
            p = p->rchild;
        }
    }

}

后序遍历：

struct node{
  int data;
  node *lchild,*rchild;
  int flag = 0;     //表示是否被访问过
};

void PostOrder(node *T)
{
    node *p = T;
    Stack s;

    while(p || isempty(s))
    {
        while(p)
        {
            push(p);
            p = p->lchild;
        }

        if(!isempty(s))
        {
             p = getTop(s);
             if(p->rchild && p->rchild->flag ==0)   //如果有右孩子，并且没有被访问过
             {
                 p = p->rchild;
             }else
             {
                 p = pop(s);
                 printf("%d",p->data);
                 p->flag = 1;
                 p = NULL;      //每次出栈一个结点，相当于遍历完以该节点为根的子树，将p置NULL
             }
        }
    }
}