#include <iostream>  //for cout
#include "date.h"
using namespace std; //because invalid_argument and cout belong to namespace std

const int date::length[] {
	 0,   //dummy, so that January will have subscript 1
	31,   //January
	28,   //February.  Pretend there are no leap years.
	31,   //March
	30,   //April
	31,   //May
	30,   //June
	31,   //July
	31,   //August
	30,   //September
	31,   //October
	30,   //November
	31    //December
};

//The constructor installs 1 valid value into a newborn date object,
//or it throws an exception.

date::date(int m, int d, int y)
	: day {365 * y + d - 1}
{
	if (m < 1 || m > 12) {
		throw invalid_argument("bad month");
	}
	if (d < 1 || d > length[m]) {
		throw invalid_argument("bad day of the month");
	}

	//Add on all the days in all the months before month m.
	for (int month {1}; month < m; ++month) {
		day += length[month];
	}
}

void date::print() const  //Can't change the date object.
{
	const int year {day / 365};
	int dayOfYear  {day % 365 + 1};  //in range 1 to 365 inclusive

	int m {1};
	for (; dayOfYear > length[m]; ++m) {
		dayOfYear -= length[m];
	}

	cout << m << "/" << dayOfYear << "/" << year;
}

void date::next(int n)     //Move this date n days into the future.
{
	day += n;          //means day = day + n
}

void date::next()          //Move this date one day into the future.
{
	++day;
}

void date::prev(int n)
{
	day -= n;          //means day = day - n
}

void date::prev()          //Move this date one day into the past.
{
	--day;
}