Swift Program to Check Leap Year

Swift – Check Leap Year

In this tutorial, we will learn how to check if a given year is a leap year in Swift. Leap years occur every 4 years, except for years that are divisible by 100 but not divisible by 400. We will implement a simple function to determine if a year is a leap year and handle edge cases.

---

What is a Leap Year?

A leap year is a year that contains an extra day, February 29, to keep the calendar year synchronized with the astronomical year. The rules to determine a leap year are:

• A year is a leap year if it is divisible by 4.
• However, if the year is divisible by 100, it is not a leap year unless it is also divisible by 400.

For example:

• 2000 is a leap year because it is divisible by 400.
• 1900 is not a leap year because it is divisible by 100 but not by 400.
• 2024 is a leap year because it is divisible by 4.

---

Algorithm to Check Leap Year

1. If the year is divisible by 400, it is a leap year.
2. If the year is divisible by 100 but not by 400, it is not a leap year.
3. If the year is divisible by 4 but not by 100, it is a leap year.
4. Otherwise, it is not a leap year.

Using this logic, we can create a function to determine if a year is a leap year.

---

Implementing Leap Year Check in Swift

Here’s a simple function to check if a year is a leap year:

func isLeapYear(_ year: Int) -> Bool {
    if year % 400 == 0 {
        return true
    } else if year % 100 == 0 {
        return false
    } else if year % 4 == 0 {
        return true
    } else {
        return false
    }
}

// Example usage
let year = 2024
if isLeapYear(year) {
    print("\(year) is a leap year.")
} else {
    print("\(year) is not a leap year.")
}

Explanation:

• year % 400 == 0: Checks if the year is divisible by 400.
• year % 100 == 0: Excludes years that are divisible by 100 but not 400.
• year % 4 == 0: Identifies years that are divisible by 4 but not by 100.

---

Handling Edge Cases

The function handles edge cases such as:

• 2000: A leap year (divisible by 400).
• 1900: Not a leap year (divisible by 100 but not by 400).
• 2023: Not a leap year (not divisible by 4).

---

Complete Swift Program

Here’s the complete program to check if a year is a leap year:

main.swift

import Foundation

// Function to check if a year is a leap year
func isLeapYear(_ year: Int) -> Bool {
    if year % 400 == 0 {
        return true
    } else if year % 100 == 0 {
        return false
    } else if year % 4 == 0 {
        return true
    } else {
        return false
    }
}

// Test cases
let years = [2000, 1900, 2023, 2024, 2100]
for year in years {
    if isLeapYear(year) {
        print("\(year) is a leap year.")
    } else {
        print("\(year) is not a leap year.")
    }
}

Output:

2000 is a leap year.
1900 is not a leap year.
2023 is not a leap year.
2024 is a leap year.
2100 is not a leap year.
Program ended with exit code: 0

This program efficiently checks if a given year is a leap year, adhering to the rules of the Gregorian calendar.