/*-- Stack.h ---------------------------------------------------------------
 
  This header file defines a Stack data type.
  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:          Retrieves the top stack value; leaves stack unchanged
    pop:          Modifies 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 
--------------------------------------------------------------------------*/

#include <iostream>

#ifndef STACK
#define STACK

const int STACK_CAPACITY = 128;
typedef int StackElement;

class Stack
{
 public:
  /***** Function Members *****/
  /***** Constructor *****/
  Stack();
  /*------------------------------------------------------------------------
    Construct a Stack object.

    Precondition:  None.
    Postcondition: An empty Stack object has been constructed (myTop is 
        initialized to -1 and myArray is an array with STACK_CAPACITY
        elements of type StackElement).
   -----------------------------------------------------------------------*/

  bool empty() const;
  /*------------------------------------------------------------------------
    Check if stack is empty.
    Precondition: None
    Postcondition: Returns true if stack is empty and false otherwise.
   -----------------------------------------------------------------------*/

  void push(const StackElement & value);
  /*------------------------------------------------------------------------
    Add a value to a stack.

    Precondition:  value is to be added to this stack
    Postcondition: value is added at top of stack provided there is space;
         otherwise, a stack-full message is displayed and execution is
         terminated.
   -----------------------------------------------------------------------*/

  void display(ostream & out) const;
  /*------------------------------------------------------------------------
    Display values stored in the stack. 

    Precondition:  ostream out is open.
    Postcondition: Stack's contents, from top down, have been output to out.
   -----------------------------------------------------------------------*/

  StackElement top() const;
  /*------------------------------------------------------------------------
    Retrieve value at top of stack (if any).

    Precondition:  Stack is nonempty
    Postcondition: Value at top of stack is returned, unless the stack is 
        empty; in that case, an error message is displayed and a "garbage
        value" is returned.
   -----------------------------------------------------------------------*/

  void pop();
  /*------------------------------------------------------------------------
    Remove value at top of stack (if any).

    Precondition:  Stack is nonempty.
    Postcondition: Value at top of stack has been removed, unless the stack
        is empty; in that case, an error message is displayed and
        execution allowed to proceed.
   -----------------------------------------------------------------------*/ 

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

#endif