#include <stdexcept>  //for class out_of_range
#include "stack.h"
using namespace std;  //because class out_of_range belongs to namespace std;

stack::stack()   //Constructor
{
	sp = a;   //Start with the stack empty.  a means &a[0]
}

void stack::push(int i)  //Insert an int into the stack.
{
	if (sp == a + n) {   //a+n means &a[n]
		//The stack is already full.
		throw out_of_range("Overflow: stack already filled to capacity");
	}
	*sp = i;  //Store i into a currently unused space.
	++sp;
}

int stack::pop() //Remove an int (the most recently inserted one) from stack.
{
	if (sp == a) {   //a means &a[0]
		//The stack is already empty.
		throw out_of_range("Underflow: can't take blood from a stone.");
	}
	--sp;       //Point at the most recently pushed value.
	return *sp; //Return the most recently pushed value.
}