//Stack.cpp

/* Stack.cpp implements some of the operations of the 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 
 ------------------------------------------------------------*/
#include <iostream>
using namespace std;
#include "Stack.h"

// Definition of push()
void Stack::push(const StackElement & value)
{
 if (myTop < STACK_CAPACITY - 1) 
 {                //Preserve stack invariant
   ++myTop;
   myArray[myTop] = value;
 }
else
   cerr << 
    "*** Stack full -- can't add new value ***\n"
    "Must increase value of STACK_CAPACITY in Stack.h\n";
}

// Definition of display()
void Stack::display(ostream & out) const
{
  for (int i = myTop; i >= 0; i--) 
    out << myArray[i] << endl;
}

// Definition of top()
StackElement Stack::top() const
{
  if (myTop >= 0)
    return (myArray[myTop]);
  else
  {
    cerr << "*** Stack is empty "
            " -- returning garbage ***\n";
    return myArray[STACK_CAPACITY-1];
  }
}