Checking Whether a Year Is a Leap Year

In this lesson you will learn how to test whether a year is a leap year in C#, covering how to combine several conditions into one decision. This is for anyone searching for "C# leap year check implementation".

A year is a leap year if it is divisible by 4 but not by 100, or if it is divisible by 400. It is basic logic that appears in calendar and date-calculation programs.

The sample code expresses this whole rule in the single expression (year % 4 == 0 && year % 100 != 0) || year % 400 == 0. 2024 is divisible by 4 and not by 100, so it is a leap year; 1900 is divisible by 100 but not by 400, so it is not.

A common stumbling block for beginners is testing only for multiples of 4. The famous examples are 2000, which is divisible by 400 and so is a leap year, and 1900, which is divisible by 100 but not 400 and so is not.

In real-world development, this leap-year logic is essential for accurate day counts whenever you implement date arithmetic or calendar features.

📖 Reference code

using System;

class Program {
    static bool IsLeapYear(int year) {
        return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
    }

    static void Main() {
        Console.WriteLine(IsLeapYear(2024));
        Console.WriteLine(IsLeapYear(2023));
        Console.WriteLine(IsLeapYear(1900));
    }
}

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