//Stack.h

/* Stack.h provides a Stack class.
 *
 * Basic operations:
 *   Constructor:  Constructs an empty stack
 *   empty:        Checks if a stack is empty
 *   push:         Modifies a stack by adding a value at the top
 *   top:          Accesses the top stack value; leaves stack
 *                   unchanged
 *   pop:          Modifies a stack by removing the value at the 
 *                   top
 *   display:      Displays all the stack elements
 * Class Invariant:
 *   1. The stack elements (if any) are stored in positions
 *      0, 1, . . ., myTop of myArray.
 *   2. -1 <= myTop < STACK_CAPACITY 
 ------------------------------------------------------------*/
#ifndef __STACK_H
#define __STACK_H

const int STACK_CAPACITY = 128;
typedef int StackElement;

class Stack
{
/***** Function Members *****/
public:
/*--- Constructor ---
  Precondition:  A stack has been declared.
  Postcondition: Stack has been constructed
                   as an empty stack.
*********************************************/
Stack();

/* --- Is the Stack empty? ---
 * Returns: true if the Stack containing this 
 *           function is empty and false otherwise
***************************************************/
bool empty() const;

/* --- Add a value to the stack ---
 *
 * Receive: A value to be added to a Stack
 * Postcondition: Value is added at top of stack 
 *                 provided there's space
 * Output:  "Stack full" message if no space 
*************************************************/

void push(const StackElement & value);

/* --- Display values stored in the stack ---
 *
 * Receive: The ostream out
 * Output:  Stack's contents, from top down, to out
 ***************************************************/
void display(ostream & out) const;

/* --- Return value at top of the stack ---
 * Return: value at the top of nonempty Stack
 * Output:  "Stack empty" message if stack empty
 ***************************************************/
 StackElement top() const;

/* --- Remove value at top of the stack ---
 * Postcondition: Top value of stack (if any) has
 *                been removed.
 * Output: "Stack-empty" message if stack is empty. 
**************************************************/
void pop();


/***** Data Members *****/
private:
  StackElement myArray[STACK_CAPACITY];
  int myTop;
}; // end of class declaration

// Definition of (default) constructor
inline Stack::Stack() { myTop = -1; }

// Definition of empty()
inline bool Stack::empty() const
{ return (myTop == -1); }

// Definition of pop()
inline void Stack::pop()
{
  if (myTop >= 0)    // Preserve stack invariant
    myTop--;
  else
    cerr << "*** Stack is empty -- "
            "can't remove a value ***\n";
}

#endif