Thread: Problems with "if " statements in terms of leap years

Hi,
I've been working in my free time on a project which tells what day someone is born based on their birthday. However, when I start to input birthdays greater than about a year old, the program is off by about a day. I believe this problem to be due to the leap year if statement I had, which I bolded in the code below. If you can offer any tips, suggestions, or hints, that would be amazing.

Code:

import java.util.Scanner;
import static java.lang.System.in;
import static java.lang.System.out;
public class DayOfBirth {
	public static void main (String args[]) {
		Scanner scanned = new Scanner (in);
		out.println("Which year were you born?");
		int birthYear = scanned.nextInt();
		out.println("What month were you born?(1 for January, 2 for February...)");
		int birthMonth = scanned.nextInt();
		out.println("What day were you born?");
		int birthDate = scanned.nextInt();
 
		int daysSince = 31 - birthDate;
		int monthsSince = 12 - birthMonth;
		int yearsSince = 2018 - birthYear;
		int leapYearsSince = yearsSince / 4;
		int monthDaysSince = 0;
		switch (monthsSince) {
		case 0:
			monthDaysSince = 0;//From end of December
			break;
		case 1:
			monthDaysSince = 31;//November
			break;
		case 2:
			monthDaysSince = 61;//October
			break;
		case 3:
			monthDaysSince = 92;//September
			break;
		case 4:
			monthDaysSince = 122;//August
			break;
		case 5:
			monthDaysSince = 153;//July
			break;
		case 6:
			monthDaysSince = 184;//June
			break;
		case 7:
			monthDaysSince = 214;//May
			break;
		case 8:
			monthDaysSince = 245;//April
			break;
		case 9:
			monthDaysSince = 275;//March
			break;
		case 10:
			monthDaysSince = 306;//February
			break;
		case 11:
			monthDaysSince = 334;//January
		}
		String day = null;
		int yearDaysSince = yearsSince * 365; 
		[B]if (leapYearsSince == 0 && birthYear % 4 == 0 && birthMonth <=2) {
			leapYearsSince++;
		}[/B]
		int daysSinceBirth = daysSince + leapYearsSince + monthDaysSince + yearDaysSince;
		int daysFromMonday = daysSinceBirth % 7;
		switch (daysFromMonday) {
		case 0:
			day = "Monday";
			break;
		case 1:
			day = "Sunday";
			break;
		case 2:
			day = "Saturday";
			break;
		case 3:
			day = "Friday";
			break;
		case 4:
			day = "Thursday";
			break;
		case 5:
			day = "Wednesday";
			break;
		case 6:
			day = "Tuesday";
			break;
		}
		out.println("You were born on a " + day + ".");
		scanned.close();
	}
 
}

I'm having a bit of trouble following how you are calculating the birthday-of-the-week. Could you explain it (in English rather than code)? Perhaps giving an example for a specific birthday: 1 Jan, 1970 or whatever.