Java Program to check if a number is a magic number or not

Java program to check if a number is a magic number or not:

In this post, we will learn how to check if a number is magic number or not. This program will get one number as input from the user and print one message either it is a magic number or it is not a magic number.

I will show you different ways to solve this problem.

What is a magic number:

A number is called a magic number if the sum of the digits of a number, if we find the sum repeatedly till we find a single digit is 1. For example, let’s check these numbers:

1234. The sum of its digits is 10. Since 10 is not one digit, we need to find the sum of the digits again which is 1 + 0 = 1, which is a one digit and equal to 1. So, it is a magic number.
1235. The sum of the digits is 11. Since 11 is not one digit, 1 + 1 is 2. So, it is not a magic number.

Method 1: Java program to check if a number is a magic number or not:

In this program, we are taking a number as input from the user and finding the sum of its digits repeatedly until it become a single digit:

import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        int no, sum = 0;
        Scanner sc = new Scanner(System.in);

        System.out.println("Enter a number: ");
        no = sc.nextInt();

        while (no > 0 || sum > 9) {
            if (no == 0) {
                no = sum;
                sum = 0;
            }
            sum += no % 10;
            no /= 10;
        }

        if (sum == 1) {
            System.out.println("It is a Magic number");
        } else {
            System.out.println("It is not a Magic number");
        }

    }
}

In this program,

no is an integer variable to hold the value of the user input number.
sum is to hold the value of the sum of digits of the number.
sc is a Scanner variable to read the user input.
It asks the user to enter a number. It reads it and stores it in the no variable.
The while loop will run till the value of no is positive or the value of sum is greater than 9, i.e. not one digit.
- If the value of no become 0, it assigns the calculated sum to no and reset the sum variable by assigning 0 to it.
- On each iteration, it gets the last digit of no by using % 10 and adds that value to sum.
- It also removes the last digit from no on each iteration.
Once the loop ends, it checks the value of sum. If it is 1, it is a Magic number, else it is not a Magic number.

If you run this program, it will print output as like below:

Enter a number: 
1235
It is not a Magic number

Enter a number: 
1234
It is a Magic number

Method 2: Check if a number is Magic number or not by using a separate method:

We can also use a separate method to check if a number is Magic number or not.

import java.util.Scanner;

class Main {
    public static boolean isMagicNumber(int no) {
        int sum = 0;
        while (no > 0 || sum > 9) {
            if (no == 0) {
                no = sum;
                sum = 0;
            }
            sum += no % 10;
            no /= 10;
        }

        return sum == 1;
    }

    public static void main(String[] args) {
        int no;
        Scanner sc = new Scanner(System.in);

        System.out.println("Enter a number: ");
        no = sc.nextInt();

        if (isMagicNumber(no)) {
            System.out.println("It is a Magic number");
        } else {
            System.out.println("It is not a Magic number");
        }
    }
}

Here,

We created a new method called isMagicNumber.
This method takes one number as the parameter and returns one boolean value.
It finds the sum of the digits of the number and returns true if it is 1, else it returns false.

It will give a similar result.

CodeVsColor

Java Program to check if a number is a magic number or not