Java Program - Check if a Number is Prime

Mathematics for Programming Numbers (Article) Numbers (Program)

This Java program checks whether a given number (in this case, 29) is a prime number. It initializes a boolean variable isPrime to true and uses a for loop to iterate from 2 to number / 2. If the number is divisible by any value in this range (number % i == 0), it sets isPrime to false and breaks out of the loop. After the loop, it prints whether the number is prime based on the value of isPrime. If isPrime remains true, the number is prime; otherwise, it is not.

Given Input:

29

Expected Output:

29 is a prime number.

Program:

public class PrimeCheck {
    public static void main(String[] args) {
        int number = 29;
        boolean isPrime = true;

        for (int i = 2; i <= number / 2; ++i) {
            if (number % i == 0) {
                isPrime = false;
                break;
            }
        }

        if (isPrime)
            System.out.println(number + " is a prime number.");
        else
            System.out.println(number + " is not a prime number.");
    }
}

Output:

29 is a prime number.

Explanation:

import java.util.Scanner;

public class PrimeCheck {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int number = scanner.nextInt();
        boolean isPrime = true;

        if (number <= 1) {
            isPrime = false;
        } else {
            for (int i = 2; i <= number / 2; ++i) {
                if (number % i == 0) {
                    isPrime = false;
                    break;
                }
            }
        }

        if (isPrime)
            System.out.println(number + " is a prime number.");
        else
            System.out.println(number + " is not a prime number.");
    }
}