Japanese Leap Year Date not showing correctly.

Hello 20579191 The issue you’re facing is due to the way the AddYears method works. When you subtract years from a DateTime object that represents February 29, and the resulting year is not a leap year, the date is changed to February 28. In your case, you’re subtracting 2018 years from February 29, 2024. The resulting year, 6, is not a leap year in the Gregorian calendar, so the date is changed to February 28. To maintain the day as 29 for a leap year, you could manually check if the original date was the 29th of February, and if the resulting year is a leap year, then set the day to 29. Here’s how you can modify your code:

using System;
using System.Globalization;

public class Demo
{
  public static void Main ()
  {
    DateTime d1 = new DateTime (2024, 02, 29, 6, 20, 40);
    int yearsToSubtract = 2018;

    // Subtract years
    DateTime d2 = d1.AddYears (-yearsToSubtract);

    // Check if original date was Feb 29 and resulting year is a leap year
    if (d1.Day == 29 && d1.Month == 2 && DateTime.IsLeapYear(d2.Year))
    {
      // Set day to 29
      d2 = new DateTime(d2.Year, d2.Month, 29, d2.Hour, d2.Minute, d2.Second);
    }

    Console.WriteLine("Initial DateTime = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss} ", d1);
    Console.WriteLine("New DateTime (subtracting years) = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss} ", d2);

    JapaneseCalendar myCal = new JapaneseCalendar();
    var s = d2.Year;
    bool r = myCal.IsLeapYear(s);

    Console.WriteLine(r);
  }
}

This code will ensure that if the original date was February 29 and the resulting year is a leap year, the day will remain as 29. Otherwise, it will be set to 28. I hope this helps.

If this helps your issue, tagging this as answered will help other community readers who may have similar questions.

Hello again. Here is a complete working example, taking also from @gekka

// Set the current culture to en-us
using System.Globalization;

System.Threading.Thread.CurrentThread.CurrentCulture = System.Globalization.CultureInfo.GetCultureInfo("en-us");

// Create a DateTime object with a specific date and time
DateTime d1 = new DateTime(2024, 02, 29, 6, 20, 40, DateTimeKind.Unspecified);
Console.WriteLine("Initial DateTime = {0:dd} {0:y}, {0:hh}:{0:mm}:{0:ss} ", d1);

// Create a JapaneseCalendar object
JapaneseCalendar myCal = new JapaneseCalendar();

// Get the era and year of the DateTime object
var eraType = myCal.GetEra(d1);
var eraYear = myCal.GetYear(d1);

// Check if the year is a leap year
bool isLeapYear = myCal.IsLeapYear(eraYear, eraType);

// Create a new DateTime object with the year from the Japanese calendar
DateTime d2 = new DateTime(eraYear, 2, 1, 0, 0, 0, DateTimeKind.Unspecified); // For format 'y' :: If Thread is Japanese culture , 'y' will be '0006年'

Console.WriteLine("New DateTime (subtracting years) = {0:dd} {1:y}, {0:hh}:{0:mm}:{0:ss}", d1, d2);
Console.WriteLine(isLeapYear);

// Create a new JapaneseCalendar object
JapaneseCalendar jpCal = new JapaneseCalendar();

// Create a new CultureInfo object with the Japanese culture and set the calendar to JapaneseCalendar
CultureInfo jpCaulture = new CultureInfo("ja-jp", false);
jpCaulture.DateTimeFormat.Calendar = jpCal;

// Output the minimum supported date and time of the Japanese calendar
Console.WriteLine();
Console.WriteLine("MinSupportedDateTime=" + jpCal.MinSupportedDateTime.ToString());
Console.WriteLine();

// Create DateTime objects for different eras
DateTime syouwa64 = new DateTime(1989, 1, 1);
DateTime heisei1 = new DateTime(1989, 1, 8);
DateTime heisei2 = new DateTime(1990, 1, 1);
DateTime heisei31 = new DateTime(2019, 4, 30);
DateTime reiwa1 = new DateTime(2019, 5, 1);

// Set the output encoding to Unicode
Console.OutputEncoding = System.Text.Encoding.Unicode;

// Output the era, year, and era name for each DateTime object
foreach (var dt in new[] { syouwa64, heisei1, heisei2, heisei31, reiwa1 })
{
    string eraName = dt.ToString("gg y", jpCaulture).Split(" ")[0];
    Console.WriteLine($"{dt:yyyy-MM-dd}, ERA={jpCal.GetEra(dt)}, {jpCal.GetYear(dt)}, EraName={eraName}");
}

The output now will be:

Initial DateTime = 29 February 2024, 06:20:40
New DateTime (subtracting years) = 29 February 0006, 06:20:40
True
MinSupportedDateTime=9/8/1868 12:00:00 AM
1989-01-01, ERA=3, 64, EraName=昭和
1989-01-08, ERA=4, 1, EraName=平成
1990-01-01, ERA=4, 2, EraName=平成
2019-04-30, ERA=4, 31, EraName=平成
2019-05-01, ERA=5, 1, EraName=令和

You should be able to modify this as needed, with the extensive comments applied. Does this answer your query?