Harshad Number Or Not In Java Program

A Harshad number (or Niven number) is an integer that is divisible by the sum of its digits. For example, 153 is a Harshad number because the sum of its digits (1 + 5 + 3 = 9) divides 153 evenly (153 % 9 == 0). In this article, you will learn how to determine if a given number is a Harshad number using a Java program.

Problem Statement

The task is to write a Java program that takes an integer as input and checks whether it is a Harshad number. This involves calculating the sum of its digits and then performing a divisibility check.

Example

If the input number is 156, the sum of its digits is 1 + 5 + 6 = 12. Since 156 % 12 == 0, 156 is a Harshad number.

Background & Knowledge Prerequisites

To understand this article, you should have a basic understanding of:

• Java syntax (variables, loops, conditional statements).
• Arithmetic operators (% for modulo, / for division, + for addition).
• Input/output operations using Scanner.

Use Cases or Case Studies

• Number Theory Education: Illustrating properties of numbers in a programming context.
• Coding Challenges: A common problem in introductory programming contests.
• Algorithm Practice: Good for practicing digit manipulation and basic conditional logic.

Solution Approaches

Approach 1: Iterative Digit Sum Calculation

This approach involves iteratively extracting each digit of the number, summing them up, and then checking for divisibility.

• One-line summary: Calculate the sum of digits using a while loop and then check if the original number is divisible by this sum.

// Harshad Number Checker
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        // Step 1: Create a Scanner object to read user input
        Scanner scanner = new Scanner(System.in);

        // Step 2: Prompt the user to enter a number
        System.out.print("Enter a number to check if it's a Harshad number: ");
        int number = scanner.nextInt();

        // Step 3: Store the original number for the divisibility check
        int originalNumber = number;
        int sumOfDigits = 0;

        // Step 4: Calculate the sum of digits
        // Use a while loop to extract digits until the number becomes 0
        while (number > 0) {
            int digit = number % 10; // Get the last digit
            sumOfDigits += digit;    // Add the digit to the sum
            number /= 10;            // Remove the last digit
        }

        // Step 5: Check if the original number is divisible by the sum of its digits
        if (sumOfDigits != 0 && originalNumber % sumOfDigits == 0) {
            System.out.println(originalNumber + " is a Harshad number.");
        } else {
            System.out.println(originalNumber + " is not a Harshad number.");
        }

        // Step 6: Close the scanner
        scanner.close();
    }
}

Run

• Sample output:

Enter a number to check if it's a Harshad number: 156
156 is a Harshad number.

• Stepwise explanation:

1. Initialize a Scanner to get input from the user.
2. Read the integer input and store it in number.
3. Create a copy of the number in originalNumber because number will be modified during digit sum calculation.
4. Initialize sumOfDigits to 0.
5. Enter a while loop that continues as long as number is greater than 0.

• Inside the loop, number % 10 extracts the last digit.
• This digit is added to sumOfDigits.
• number /= 10 removes the last digit from number, effectively shifting the number to the right.

1. After the loop, check if sumOfDigits is not zero (to avoid division by zero) and if originalNumber is perfectly divisible by sumOfDigits using the modulo operator (%).
2. Print the appropriate message indicating whether the number is a Harshad number.
3. Close the Scanner to prevent resource leaks.

Conclusion

Determining if a number is a Harshad number is a straightforward programming task that combines basic arithmetic operations with loop structures. The iterative approach of summing digits is efficient and easy to understand, making it suitable for this problem.

Summary

• A Harshad number is divisible by the sum of its digits.
• To check for a Harshad number:
• Calculate the sum of its digits.
• Check if the original number is perfectly divisible by this sum.
• The modulo operator (%) and integer division (/) are key for digit extraction.