Java Program to Check Neon Number

A neon number is a number where the sum of digits of its square is equal to the number itself.

For example, 9 is a neon number because 9² = 81 and 8 + 1 = 9.

1. Understanding the Problem

Determine whether a given number is a neon number.

Number: 9 → Neon
Number: 1 → Neon
Number: 10 → Not Neon

2. Using Basic Loop

              
            
Java

          Check neon number using loop
        
import java.util.Scanner;

public class NeonNumber {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = sc.nextInt();

        int square = num * num;
        int sum = 0;

        while (square != 0) {
            int digit = square % 10;
            sum += digit;
            square /= 10;
        }

        if (sum == num)
            System.out.println("Neon Number");
        else
            System.out.println("Not a Neon Number");
    }
}

3. Optimized Approach

              
            
Java

          Check neon number with simplified logic
        
import java.util.Scanner;

public class NeonOptimized {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int num = sc.nextInt();

        int square = num * num;
        int sum = 0;

        for (; square > 0; square /= 10) {
            sum += square % 10;
        }

        if (sum == num)
            System.out.println("Neon Number");
        else
            System.out.println("Not a Neon Number");
    }
}

4. Common Mistakes

1. Forgetting to square the number.

2. Incorrect digit extraction from square.

3. Not resetting sum properly.

4. Confusing with Armstrong number logic.

5. Applications

1. Helps in understanding number transformations.

2. Useful for practicing loops and arithmetic operations.

3. Common beginner-level coding problem.

Conclusion

Neon number programs are simple and useful for practicing digit-based logic.

They help build a strong foundation in loops and number manipulation.