用两个栈实现队列

队列声明如下：

template <typename T>
class CQueue
{
public:
	CQueue();
	~CQueue();
	void appendTail(const T& node)
	T deleteHead();
private:
	stack<T> stack1;
	stack<T> stack2;
};

template <typename T>
void CQueue<T>::appendTail(const T& node)
{
	stack1.push(node);
}

template <typename T>
T CQueue<T>::deleteHead()
{
	if (stack2.size() <= 0)
	{
		while (stack1.size() > 0)
		{
			T& data = stack1.top();
			stack1.pop();
			stack2.push(data);
		}
	}
	if (stack2.size() == 0)
		throw new exception("Queue is empty.");
	T head = stack2.top();
	stack2.pop();
	return head;
}