Leap Year Check - JavaScript Program

// Leap year rules: // 1. Divisible by 4 → Leap year // 2. BUT if divisible by 100 → NOT leap year // 3. UNLESS divisible by 400 → Leap year function isLeapYear(year) { 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 console.log("2000:", isLeapYear(2000) ? "Leap year" : "Not leap year"); console.log("1900:", isLeapYear(1900) ? "Leap year" : "Not leap year"); console.log("2024:", isLeapYear(2024) ? "Leap year" : "Not leap year"); console.log("2023:", isLeapYear(2023) ? "Leap year" : "Not leap year"); // Method 2: Single expression function isLeapYear2(year) { return (year % 400 === 0) || (year % 4 === 0 && year % 100 !== 0); } console.log("\nUsing single expression:"); console.log("2000:", isLeapYear2(2000)); console.log("1900:", isLeapYear2(1900)); console.log("2024:", isLeapYear2(2024)); // Method 3: Using ternary function isLeapYear3(year) { return year % 400 === 0 ? true : year % 100 === 0 ? false : year % 4 === 0 ? true : false; } console.log("\nUsing ternary:"); console.log("2000:", isLeapYear3(2000)); console.log("2023:", isLeapYear3(2023));

This program demonstrates leap year logic with multiple conditions.

Leap Year Rules

A year is a leap year if:

It's divisible by 400 → ## Leap year
OR it's divisible by 4 BUT NOT by 100 → ## Leap year
Otherwise → ## Not a leap year

Examples:

2000: Divisible by 400 → ✅ Leap year
1900: Divisible by 100 but not 400 → ❌ Not leap year
2024: Divisible by 4, not by 100 → ✅ Leap year
2023: Not divisible by 4 → ❌ Not leap year

Method 1: If-Else Chain

Clear, step-by-step logic:

javascript
if (year % 400 === 0) return true;
else if (year % 100 === 0) return false;
else if (year % 4 === 0) return true;
else return false;

Method 2: Single Expression

Combining conditions with logical operators:

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

Logical Operators:

||: OR - at least one true
&&: AND - both must be true
!: NOT - reverses boolean

Method 3: Nested Ternary

Compact but less readable:

javascript
return year % 400 === 0 ? true : 
       year % 100 === 0 ? false : 
       year % 4 === 0 ? true : false;

Why Leap Years?

Earth's orbit: ~365.25 days
Extra 0.25 days accumulate
Every 4 years: +1 day (February 29)
Exception: Century years need 400 rule

When to Use:

If-else: Most readable, learning
Single expression: Concise, efficient
Ternary: Compact, but harder to read

Output