Introduction

An Armstrong number (also known as a narcissistic number) is a number that is equal to the sum of its own digits, each raised to the power of the number of digits. For example, 153 is an Armstrong number because (1^3 + 5^3 + 3^3 = 153). This guide will show you how to create a Java program to check whether a given number is an Armstrong number.

Problem Statement

Create a Java program that takes an integer input from the user and checks if the number is an Armstrong number.

Example 1:

Input: 153
Output: 153 is an Armstrong number.

Example 2:

Input: 9474
Output: 9474 is an Armstrong number.

Example 3:

Input: 123
Output: 123 is not an Armstrong number.

Solution Steps

Take Input: Get the number from the user.
Calculate the Number of Digits: Determine the number of digits in the input number.
Compute the Sum of Digits Raised to Power: Raise each digit to the power of the total number of digits and compute the sum.
Check for Armstrong Number: Compare the computed sum to the original number.
Output the Result: Display whether the number is an Armstrong number.

Java Program

import java.util.Scanner;

/**
 * Java Program to Check Armstrong Number
 * Author: https://www.javaguides.net/
 */
public class ArmstrongNumberChecker {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Step 1: Take input from the user
        System.out.print("Enter a number: ");
        int number = scanner.nextInt();

        // Step 2: Calculate the number of digits
        int numberOfDigits = String.valueOf(number).length();

        // Step 3: Compute the sum of digits raised to the power of numberOfDigits
        int sum = 0;
        int temp = number;
        while (temp > 0) {
            int digit = temp % 10;
            sum += Math.pow(digit, numberOfDigits);
            temp /= 10;
        }

        // Step 4: Check if the sum is equal to the original number
        if (sum == number) {
            System.out.println(number + " is an Armstrong number.");
        } else {
            System.out.println(number + " is not an Armstrong number.");
        }
    }
}

Step by Step Explanation

Take Input: The program starts by prompting the user to enter a number.
Calculate the Number of Digits: The String.valueOf(number).length() is used to determine the number of digits in the input number. For example, if the input is 153, the number of digits is 3.
Compute the Sum of Digits Raised to Power:
- A temporary variable temp is used to store the original number.
- The program iterates through each digit of the number by using the modulus operator % and integer division /.
- For each digit, the program raises it to the power of numberOfDigits and adds the result to sum.
- The loop continues until all digits have been processed.
Check for Armstrong Number: After the loop, the sum of the digits raised to their respective powers is compared to the original number.
Output the Result: If the sum equals the original number, it is an Armstrong number. Otherwise, it is not.

Output Examples

Example 1:

Enter a number: 153
153 is an Armstrong number.

Example 2:

Enter a number: 9474
9474 is an Armstrong number.

Example 3:

Enter a number: 123
123 is not an Armstrong number.

Conclusion

This Java program effectively checks whether a given number is an Armstrong number. The key steps involve calculating the number of digits, raising each digit to the power of the number of digits, summing these values, and comparing the sum to the original number. This program can be easily extended to check Armstrong numbers of different lengths or for different bases.