Armstrong Number in Java | Print Armstrong Number between 1 to 1000

An Armstrong Number is a number which is equal to the sum of its owns digits, each of them raised to the power of the total number of digits. In this article, Let’s write a program check whether the given number is Armstrong Number in Java.

What is an Armstrong Number?

A number is said to be an Armstrong Number, whenever it satisfies the below condition.

xyz = xⁿ + yⁿ + zⁿ

n represents the number of digits.

Let’s understand with a pretty common example, 153 is an Armstrong number because it satisfies the condition sum of its digits raised to the power of the number of digits of that number should be equal to the actual number

153 = 1³ + 5³ + 3³

Total number digit is 3 and hence the power is 3

1³ = 1
5³ = 125
3³ = 27

1 + 125 + 27 = 153

Similarly 1634 is an Armstrong, 1634 => 1⁴ + 6⁴ + 3⁴ + 4⁴ => 1 + 1296 + 256 + 81  => 1634

Let’s get into the coding

Program 1: Java Program to Check Armstrong Number using While Loop

package com.javainterviewpoint;

import java.util.Scanner;

public class ArmstrongNumber
{
    public static void main(String[] args)
    {
        Scanner scanner=new Scanner(System.in);
        System.out.println("Enter a number to check for Armstrong");
        
        int actualNumber = scanner.nextInt();
        int temp = actualNumber;
        int remainder = 0;
        int sum = 0;
        int n = 0;
        
        // Get the total number of digits
        while(temp != 0)
        {
            temp = temp / 10;
            n++;
        }
        temp = actualNumber;
        
        // Check for Armstrong Number
        while(temp != 0)
        {
            remainder = temp  % 10;
            sum = (int) (sum + Math.pow(remainder, n));
            temp = temp / 10;
        }
        
        if(actualNumber == sum)
            System.out.println(actualNumber + " is an Armstrong Number");
        else
            System.out.println(actualNumber + " is not an Armstrong Number");
    }
}

• Get the number which needs to be checked from the user using the Scanner instance and store it in the variable actualNumber.
• Store the input (actualNumber) in a temp variable, it is a necessary step to make a copy of the original number, because temp variable gets changed during the execution of the program and towards the end, we need the original input number for validation
• Now we need to know the number of digits in the input number, in a while loop divide the temp value by 10 for each iteration increment the value of n, the loop continues till the value of temp is not equal to zero.

while(temp != 0)
{
      temp = temp / 10;
      n++;
}

• Alternatively, we can get the number of digits in a simple way, just add an empty string and use the length() method to get the number of digits.

n = (actualNumber + “”).length();

• Since the temp value will be zero now, we need to reassign it with the actualNumber
• Now in a while loop, we need to extract the digits from right to left and raise them with the power of the number of digits. To get the individual numbers, divide the temp value by 10 using modulo operator [This gives us the remainder in the order of right to left]
• Raise the remainder to the power of n using Math.pow() method, this method returns a double value we need to explicitly cast it to int so that we can add it to the existing sum.
• In order to truncate the last digit, we need to divide the temp value by 10 and assign it back to temp. The while loop continues to execute until the value of temp is zero.
• Finally, check whether the actualNumber and sum are equal, if so, then the number is Armstrong.

Output:

Enter a number to check for Armstrong
123
123 is not an Armstrong Number

Program 2: Armstrong Number in Java using For Loop

While loop checks for the Armstrong Numbers in the above program

Now let’s try to use For loop for doing the same validation

package com.javainterviewpoint;

import java.util.Scanner;

public class ArmstrongNumber
{
    public static void main(String[] args)
    {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter a number to check for Armstrong");
        int actualNumber = scanner.nextInt();
        int temp = actualNumber;
        int remainder = 0;
        int sum = 0;
        int n = 0;
        // Get the total number of digits
        n = (temp + "").length();
        
        // Check for Armstrong Number
        for(; temp > 0; temp /=10)
        {
            remainder = temp % 10;
            sum = (int) (sum + Math.pow(remainder, n));
        }
        
        if (actualNumber == sum)
            System.out.println(actualNumber + " is an Armstrong Number");
        else
            System.out.println(actualNumber + " is not an Armstrong Number");
    }
}

There are only two changes which we have made

• Get the number of digits by simply appending the temp value with an empty string and call length() method on top of it get the total number of digits
• Using for loop to perform the iteration, we have not assigned the initialization value, the loop will continue to execute until the value temp is greater than zero

Program 3: Java Program to Print Armstrong Number between 1 to 1000

In this Java program, we will take the start and end value from the user and print all the possible Armstrong numbers.

package com.javainterviewpoint;

import java.util.Scanner;

public class ArmstrongNumber
{
    public static void main(String[] args)
    {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the start value : ");
        int start = scanner.nextInt();
        System.out.println("Enter the end value : ");
        int end = scanner.nextInt();
        
        System.out.println("*** Printing the List of Armstrong Numbers ***");
        for(int i=start; i<=end; i++)
        {
            if(checkArmstrong(i))
                System.out.println(i);
        }
    }
    
    public static boolean checkArmstrong (int value)
    {
        int temp = value;
        int remainder = 0;
        int sum = 0;
        int n = 0;
        // Get the total number of digits
        n = (temp + "").length();
        
        // Check for Armstrong Number
        while (temp != 0)
        {
            remainder = temp % 10;
            sum = (int) (sum + Math.pow(remainder, n));
            temp = temp / 10;
        }
        
        if (value == sum)
            return true;
        else
            return false;
    }
}

Output:

Enter the start value : 
1
Enter the end value : 
1000
*** Printing the List of Armstrong Numbers ***
1
2
3
4
5
6
7
8
9
153
370
371
407

Although we have used the above code to print from 1 to 1000, the code works fine for any definitive ranges.

Happy Learning !!