#pragma once
#include "stack.h"

class Calculator
{
public:

	double value; //calculator's current value
	stack history;

	Calculator()
	{
		value =0;
	}

	Calculator(double x)
	{
		value = x;
	}

	void clear()
	{
		history.push(value);
		value = 0;
	}

	void add(double x)
	{
		history.push(value);
		value = value + x; //equivalent: value += x;
	}

	void divide(double x)
	{
		history.push(value);
		value = value / x; //or: value /= x;
	}

	void multiply(double x)
	{
		history.push(value);
		value = value * x;  //or: value *= x;
	}

	void subtract(double x)
	{
		history.push(value);
		value = value - x; //or: value -= x;
	}

	void undo()
	{
		value = history.pop();
	}

	double display()
	{
		return value;
	}
};