A leap year is exactly divisible by 4 except for century years (years ending with 00). The century year is a leap year only if it is perfectly divisible by 400.

Example 1: Kotlin Program to Check a Leap Year using if else statement

fun main(args: Array<String>) {

    val year = 1900
    var leap = false

    if (year % 4 == 0) {
        if (year % 100 == 0) {
            // year is divisible by 400, hence the year is a leap year
            leap = year % 400 == 0
        } else
            leap = true
    } else
        leap = false

    println(if (leap) "$year is a leap year." else "$year is not a leap year.")
}

When you run the program, the output will be:

1900 is not a leap year.

In the above program, given year 1900 is stored in the variable year.

• Since 1900 is divisble by 4 and is also a century year (ending with 00), it has be divisble by 400 for a leap year. Since it’s not divisible by 400, 1900 is not a leap year.
• But, if we change the year to 2000, it is divisible by 4, is a century year and is also divisible by 400. So, 2000 is a leap year.
• Likewise, If we change the year to 2012, it is divisible by 4 and is not a century year, so 2012 a leap year. We don’t need to check if 2012 is divisible by 400 or not.

Example 2: Kotlin Program to Check Leap Year using when expression

fun main(args: Array<String>) {

    val year = 2012
    var leap = false

    leap = when {
        year % 4 == 0 -> {
            when {
                year % 100 == 0 -> year % 400 == 0
                else -> true
            }
        }
        else -> false
    }

    println(if (leap) "$year is a leap year." else "$year is not a leap year.")
}

When run the program, the output will be:

2012 is a leap year.

In the above program, instead of using an if else statement, we have used a when expression.

The when expression works as:

• When year is divisible by 4
  • Another when expression is entered which checks if year is divisible by 100
    • If yes, it again checks if year is divisble by 400 or not, and returns true or false
  • If not divisble by 100, year is not a century year (ending with 00) and returns true
• If year is not divisible by 4, it returns false

Based on the value of leap, it prints the output using an inline if else.