//A year is a leap year if it is divisible by 4.

//However, if the year is also divisible by 100, it is not a leap year unless:

//The year is also divisible by 400, in which case it is a leap year.

using System;

​

public class Program

{

    public static void Main()

    {

        int[] testYears =

        {

            1600,

            1700,

            1800,

            1900,

            2000,

            2004,

            2010,

            2020,

            2021,

            2024

        };

        foreach (int year in testYears)

        {

            bool leap = ToTestLeap(year);

            Console.WriteLine($"{year} is {(leap ? "a Leap year" : "not a leap year")}");

        }

    }

​

    public static bool ToTestLeap(int year)

    {

        /*      

        if (year % 4 == 0)

        {

            if (year % 100 == 0)

            {

                if (year % 400 == 0)

                {

                    if (year % 400 == 0)

            {

                return true; // Divisible by 400 -> Leap year

            }

            return false; // Divisible by 100 but not by 400 -> Not a leap year

        }

        return true; // Divisible by 4 but not by 100 -> Leap year

    }

    return false; // Not divisible by 4 -> Not a leap year

    }

*/

        return (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0);

    }

}