// This will probably not compile. Its up to you to learn how to code.
// ~Phil

#define JAN		1
#define	FEB		2
#define MAR		3
#define	APR		4
#define	MAY		5
#define	JUN		6
#define JUL		7
#define	AUG		8
#define	SEP		9
#define	OCT		10
#define	NOV		11
#define	DEC		12
#define MIN_YEAR	1582

bool validMonth(int month) {
	// Very verbose method
	// Creates a variable for storing the return value
	// then sets it as true or false
	// then returns the (set) variable
	bool valid;
	if (month >= JAN || month <= DEC) {
		valid = true;
	} else {
		valid = false;
	}
	return valid;
}

bool validYear(int year) {
	// Very direct value
	// No variable needed as the calculated value
	// is immediately returned
	return (year > MIN_YEAR);
}

bool leapYear(int year)
	// Note: The "%" is the mathematical "mod" function
	// Look this up to understand how this works and
	// why this works for this purpose.
	// I've also added gratuitous parentethese so its easier
	// to understand but know that they aren't all needed
	// return year % 4 == 0 && !(year % 100 == 0 && year % 400 !0 0);
	return ((year % 4 == 0) && !((year % 100 == 0) && (year % 400 != 0)));
}

bool validDay(int year, int month, int day) {
	// Approach:
	// Check all the "false" conditions
	// If any of these conditions trigger, immediately return false
	// If the function reaches the end, that means all
	// the "false" conditions were not met, so only then can you return true

	// Check for bad year/month
	if (!validMonth(month) || !validYear(year))
		return false;

	// Check for bad day
	switch (month) {
		// Since there's no "break" between these cases,
		// they all "fall through" and execute the same code
		case APR:
		case JUN:
		case SEP:
		case NOV:
			// 31 days
			if (day < 1 || day > 31)
				return false;
			break;
		// February is the special case
		case FEB:
			if (leapYear(year)) {
				if (day < 1 || day > 29)
					return false;
			} else {
				if (day < 1 || day > 28)
					return false;
			}
			break;
		// "default" is all the other months
		default:
			if (day < 1 || day > 30)
				return false;
			break;
	}

	// If your code has reached this point, it means the day is valid
	// This is the function you want to thoroughly check with every
	// single bad case you can think of, then some random good cases
	return true;
}

void getData(int& month, int& day, int& year) {
	// You figure this out, this will always be something language-specific.
	// Know though that this function takes POINTERS to variables as its arguments
	// meaning that when you manipulate the variables locally, you're actually
	// manipulating the original variables.
	// e.g.
	//		int a = 1;
	//		int b = 2;
	//		add(&a, &b);
	// After this, a = 3, b = 2
	// BUT
	//		int a = 1;
	//		int b = 2;
	//		add(a, b);
	// After this, a = 1, b = 2
	// This is a bad example and depends on
	// how "add" is implemented, but you get the idea - see your textbook for examples
}

void easterDate(int& month, int&day, int year) {
	// Exactly as the instructions say. Use "/" and "%".
}

int daysBetween(int month1, int day1, int month2, int day2, int year) {
	return dayOfYear(day2, month2, year) - dayOfYear(day1, month1, year);
}

int dayOfYear(int day, int month, int year) {
	int value;

	// Add months values
	// We can do this because we know the set values
	// Deal with leap year later
	// Note: Yes, this can be a bunch of "if" statements followed by each other
	// that step-by-step adds things up, but a single switch statement is
	// MUCH MUCH faster since it allows for compile-time calculated values
	// and has less checks
	switch(month) {
		case JAN:
			break;
		case FEB:
			value += (31);
			break;
		case MAR:
			value += (31 + 28);
			break;
		case APR:
			value += (31 + 28 + 31);
			break;
		case MAY:
			value += (31 + 28 + 31 + 30);
			break;
		case JUN:
			value += (31 + 28 + 31 + 30 + 31);
			break;
		case JUL:
			value += (31 + 28 + 31 + 30 + 31 + 30);
			break;
		case AUG:
			value += (31 + 28 + 31 + 30 + 31 + 30 + 31);
			break;
		case SEP:
			value += (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31);
			break;
		case OCT:
			value += (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30);
			break;
		case NOV:
			value += (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31);
			break;
		case DEC:
			value += (31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30);
			break;
	}

	// Check leap-years
	if (leapYear(year) && month > 2) {
		value += 1;
	}

	// Add the actual day
	value += day;

	// Return calculated value
	return value;
}

int main() {
	bool loop = true;
	string command;
	int month1, day1, month2, day2, year;
	int dayDiff;

	// Somewhere in here you should check when the user wants to exit
	// and if found, set loop to false.
	// The easiest way would be to change getData to return a bool
	// (which is false if the user indicates he wants to exit)
	// and set loop to the returned bool
	while (loop){
		command = getCommand(); // Some prompt, this is an example
		// Here we just use a series of "if-else" because there
		// aren't many cases and each is very different
		if (strcmp(command, "exit") == 0) {
			loop = false;
		} else if (strcmp(command, "day") == 0) {
			getData(&month1, &day1, &year); // Overload getData or made a new function
			if (!validDay(year, month1, day1)) {
				// print error
			} else {
				// print dayOfYear(day1, month1, year);
			}
		} else if (strcmp(command, "easter") == 0) {
			getData(&year);
			easterDate(&month1, &day1, year);
			// print month and day
		} else if (strcmp(command, "diff") == 0) {
			getData(&month1, &day1, &month2, &day2, &year);
			dayDiff = daysBetween(month1, day1, month2, day2, year);
			if (dayDiff < 0) {
				// print error
			} else {
				// print dayDiff
			}
		}
	}

	// print exit message
}