/* 
 *  File: stack.cpp
 *        Member functions implementations for a Stack ADT 
 *
 *  From Dr. Mateen Rizki
 *  Modified: spc
 * 
 * CLASS INVARIANT
 * 1.  If the stack is empty, the top of stack is undefined
 * 2.  If the stack is non-empty, top_node holds address of top node of stack
 */

#include "stack-rizki.h"

template <class Stack_entry>
stack<Stack_entry>::stack()
{
   top_node = 0;
}

template <class Stack_entry>
void stack<Stack_entry>::push(const Stack_entry &item)
{
	node *temp = new node;
	if (temp == NULL)
		throw string("bad allocation");

	temp->data = item;
	temp->next = top_node;
	top_node = temp;
}

template <class Stack_entry>
void stack<Stack_entry>::pop()
{
	if (empty())
		throw string("stack underflow");

	node *temp = top_node;
	top_node = top_node->next;
	delete temp;
}

template <class Stack_entry>
Stack_entry stack<Stack_entry>::top() const
{
	if (empty())
		throw string("stack underflow");

	return top_node->data;
}

template <class Stack_entry>
bool stack<Stack_entry>::empty() const
{
   return top_node == 0;
}


        template class stack<int>;
         template class stack<char>;