Program to check a year is leap year or not.

Problem Description

1. If a year is divisible by 4, then it is called leap year.
2. But all the centuries are divisible by 4, so to check a century is a leap year or not, we check divisibility by 400 of a year.
3. If a century is divisible by 400 then the century is called leap year otherwise not.

Basic Logic Snippets (In C)

if(year % 100 == 0) {
 if (year % 400 == 0) {
  printf("%d is a leap year",year);
 } else {
  printf("%d is not a leap year",year);
 }
}else {
 if(year % 4 == 0) {
  printf("%d is a leap year",year);
 } else {
  printf("%d is not a leap year",year);
 }
}

Output

Test-1

Enter any year: 1996
1996 is a leap year

Test-2

Enter any year: 1600
1600 is a leap year

Test-3

Enter any year: 1800
1800 is not a leap year

Improved your logic

Note: Generate wrong output in some cases, but helpful to understand upcoming logic

if(year % 100 == 0 && year % 400 ==0 || year % 4 == 0) {
  printf("%d is a leap year",year);
 } else {
  printf("%d is not a leap year",year);
 }

1. Above program generates correct output in the case of 1600 and 1996 but generates wrong output in the case of 1800
2. In the case of 1800, year is century but not divisible by 400, so condition (year%100 == 0 && year%400 ==0), evalutes as false. and the next condition combined with OR(||) operator means (year%4==0) is evaluted and evalutes true.
3. But the second condition (year%4==0) should be evalutes only when year is not a century so the above program snippet generates wrong output in some cases.
4. Above program snipped problem can be fixed as shown in the following program snippet.

if(year % 100 == 0 && year % 400 ==0 || year%100!=0 && year % 4 == 0) {
  printf("%d is a leap year",year);
 } else {
  printf("%d is not a leap year",year);
 }

1. As shown in the above program snippet now condition (year%4==0), only evalutes if year is not a century and it confirmed by the condition year%100!=0
2. But as we know, 100 is one of the factor of 400, so if a thing is divisible by 400 then also divisible by 400, so the final version of above program snippet is as given below.

if(year % 400 ==0 || year%100!=0 && year % 4 == 0) {
  printf("%d is a leap year",year);
 } else {
  printf("%d is not a leap year",year);
 }

C Program

#include<stdio.h>
int main() {
 int year;
 
 printf("Enter any year: ");
 scanf("%d",&year);
 
 if(year % 400 ==0 || year%100!=0 && year % 4 == 0) {
  printf("%d is a leap year",year);
 } else {
  printf("%d is not a leap year",year);
 }
 return 0;
}

C++ Program

#include<iostream>
using namespace std;
int main() {
 int year;
 
 cout << "Enter any year: ";
 cin >> year;
 
 if(year % 400 ==0 || year%100!=0 && year % 4 == 0) {
  cout << year << " is a leap year";
 } else {
  cout << year << " is not a leap year";
 }
 return 0;
}

Java Program

import java.util.Scanner;
class IsLeapYear {
 public static void main(String args[]) {
  int year;
  
  Scanner sc = new Scanner(System.in);
  System.out.print("Enter any year: ");
  year = sc.nextInt();
  
  if(year%400 ==0 || year%100!=0 && year%4==0) {
   System.out.println(year+" is a leap year");
  }else {
   System.out.println(year+" is not a leap year");
  }
  
 }
}

Go Lang

package main
import "fmt"

func main() {
 var year int
 
 fmt.Print("Enter any year: ")
 fmt.Scan(&year)
 
 if year % 400 == 0 || year % 100 != 0 && year % 4 == 0 {
  fmt.Print(year," is a leap year")
 } else {
  fmt.Print(year," is not a leap year")
 }
}

PHP

if(isset($_POST['sub'])) {
 $year = $_POST['year'];

 if($year % 400 == 0 || $year % 100 != 0 && $year % 4 == 0) {
  echo $year." is a leap year";
 } else {
  echo $year." is not a leap year";
 }
}