在建立二叉樹的時候，當節點為葉子節點，需要將葉子節點的兩個子節點輸入0，以0作為結束識別符號。

1.建立二叉樹的結構體

typedef struct tree* bintree;
typedef bintree position;
struct tree {
	int data;
	position lchild;
	position rchild;
};

bintree creattree()
{
	int ch;
	bintree t;
	cin >> ch;
	if (0 == ch)
	{
		t = NULL;
	}
	else
	{
		t = (struct tree*)malloc(sizeof(struct tree));
		t->data = ch;
		t->lchild=creattree();
		t->rchild=creattree();
	}
	return t;
}
 

void pre_display(bintree head)
{
	if (head)
	{
		cout << head->data << ' ';
		pre_display(head->lchild);
		pre_display(head->rchild);

	}

}
void inorder_display(bintree head)
{
	if (head)
	{
		inorder_display(head->lchild);
		cout << head->data << ' ';
		inorder_display(head->rchild);
	}
}
 

int main()
{
	bintree head;
	bintree p;
	head = NULL;
	p=creattree();
	pre_display(p);
	system("PAUSE");
}