/* FILE: stack.c
 * PURPOSE:
 *    Functions that implement a simple stack.
 *    (CST 8152 - 98W - Assignment 6)
 * HISTORY:
 *    Ian D. Allen   idallen@freenet.carleton.ca
 */

//FIXME-- add system includes here
//FIXME-- add your local includes here

/* The stack structure element, containing the Item structure.
 * The stack is a singly-linked list of structures with the most
 * recent element at the head of the list.
 */
typedef struct Element {
	Item item;
	struct Element *next;
} Element;

static Element *head;		/* head of stack element list */

/* FUNCTION: push
 * PURPOSE:
 *    Allocate memory for a new stack element, copy the passed Item
 *    into the element, and push the element on the stack.
 *    Failure to allocate memory is fatal; no error status is returned.
 */
	void
push(
	Item *item	/* IN: pointer to item to push on stack */
){
//FIXME-- allocate memory for a new stack element "E"
//FIXME-- copy the passed Item into the new element "E"
//FIXME-- point "E" to the first element in the stack
//FIXME-- point the head pointer at the new element "E"
}

/* FUNCTION: pop
 * PURPOSE:
 *    Pop the stack and return an Item to the caller.
 *    An attempt to pop an empty stack is fatal.
 *    Remember to free the popped memory.
 */
	Item
pop(void){	/* RET: popped item */
	Element e;  /* copy of top element on stack */

	if( empty() ){
		eprintf("Error: POP called at stack bottom");
		abort();
		/*NOTREACHED*/
	}
//FIXME-- pick up a copy of the head element on the stack
//FIXME-- free the element pointed to by the head pointer
//FIXME-- point the head pointer at the next element in the stack

	return e.item;    /* return the Item we popped */
}

/* FUNCTION: empty
 * PURPOSE:
 *    Return TRUE if the stack is empty.
 */
	Boolean
empty(void){	/* RET: TRUE if stack is empty */
	return (head == NULL);
}