#include <stdlib.h> // Provides size_t
#include <assert.h> // Provides assert
template <class Item>
class Stack
{
    public:
        enum { CAPACITY = 64 }; // See page 99 for a better alternative
        Stack( ) { used = 0; }  // CONSTRUCTOR
        void push(const Item& entry); // MODIFICATION functions
        Item pop( );
        size_t size( ) const { return used; }
        bool is_empty( ) const { return used == 0; }
        Item peek( ) const;
    private:
        Item data[CAPACITY];  // Partially-filled array
        size_t used;          // How much of array is being used
};

template <class Item>
void Stack<Item>::push(const Item& entry)
{
    assert(size( ) < CAPACITY);
    data[used] = entry;
    used++;
}

template <class Item>
Item Stack<Item>::pop( )
{
    assert(!is_empty( ));
    used--;
    return data[used];
}

template <class Item>
Item Stack<Item>::peek( ) const
{
    assert(!is_empty( ));
    return data[used-1];
}