using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

  public static void Main()

  {

    var today = DateTime.Today;

    IsDayOfTheProgrammer(today.AddDays(-1)); // 09/12/2021

    IsDayOfTheProgrammer(today); // 09/13/2021

    IsDayOfTheProgrammer(today.AddYears(3).AddDays(-1)); // 09/12/2024: Leap year

    IsDayOfTheProgrammer(today.AddYears(3)); // 09/13/2024

  }

​

  private static void IsDayOfTheProgrammer(DateTime date)

  {

    var dayToCheck = DateTime.IsLeapYear(date.Year) ? 12 : 13;

    var monthToCheck = 9;

​

    if (date.Month == monthToCheck && date.Day == dayToCheck)

    {

      Console.WriteLine(date.ToShortDateString() + " is programmer's day.");

    }

    else

    {

      Console.WriteLine(date.ToShortDateString() + " is not programmer's day.");

    }

  }

}

​