Computer question from java

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WAP to input a number, check and print if it a MAGIC number or not. To find out if a
number is a MAGIC number or not add its digits. Now add the digits of the sum obtained.

Repeat this process till you get a single digit number. If you get 1 in the end the given
number is a MAGIC number without using boolean, return,String[] args and return statement for the isHappyNumber() method: and isHappyNumber(number))

What I have tried:

import java.util.*;
 class b1
{ public static void main ()
    {Scanner sc= new Scanner(System.in);
        int sum = 0;
    System.out.print("Enter a Number");
    int n=sc.nextInt();
    do {
     int c=n%10;
     int s=c*c;
      sum = sum+s;
       n=n/10;
    }
    while(sum==1);
    {if(sum==1)
    System.out.print("It is a Happy Number");
    else
    System.out.print("It is not a Happy Number");
    }}
}

Posted 11-Jul-23 21:31pm

Maanya Agarwal

Updated 11-Jul-23 23:16pm

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Richard MacCutchan 12-Jul-23 5:16am

You are summing the squares of each digit, which is not what the question asks.

2 solutions

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Andre Oosthuizen · Answer 1 · 2023-07-11T23:16:00

The below should solve your problem, see fiddle at - Computer question from java [^]

JavaScript

import java.util.Scanner;

public class Main {
    //To compile properly I added 'public static void main' as I am not sure if you have a public class with name 'Main'' 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int sum = 0;
        System.out.print("Enter a Number: ");
        int n = sc.nextInt();
        do {
            //Get the last digit of the number
            int c = n % 10; 
            //Square the digit
            int s = c * c; 
            //Add the squared digit to the sum
            sum = sum + s; 
            //Remove the last digit from the number
            n = n / 10; 
            //Repeat until the sum becomes a single-digit number
        } while (sum > 9); 
        
        if (sum == 1) {
            System.out.print("It is a Happy Number");
        } else {
            System.out.print("It is not a Happy Number");
        }
    }
}

With the above, keep in mind that the code will error if you have a number that exceeds the range of the 'int' data type in Java (i.e. 11111111111112), which is limited to the range -2,147,483,648 to 2,147,483,647. You then need to use the 'long' data type instead. To use 'long' -

JavaScript

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long sum = 0;
        System.out.print("Enter a Number: ");
        long n = sc.nextLong();
        do {            
            long c = n % 10; 
            long s = c * c; 
            sum = sum + s; 
            n = n / 10; 
        } while (sum > 9); 
        
        if (sum == 1) {
            System.out.print("It is a Happy Number");
        } else {
            System.out.print("It is not a Happy Number");
        }
    }
}

OriginalGriff · Answer 2 · 2023-07-11T21:52:00

First off, indent you code properly: pick a style and be consistent - it makes your code more readable:

Java

import java.util.*;
class b1 {
   public static void main() {
      Scanner sc = new Scanner(System.in);
      int sum = 0;
      System.out.print("Enter a Number");
      int n = sc.nextInt();
      do {
         int c = n % 10;
         int s = c * c;
         sum = sum + s;
         n = n / 10;
      }
      while (sum == 1); {
         if (sum == 1)
            System.out.print("It is a Happy Number");
         else
            System.out.print("It is not a Happy Number");
      }
   }
}

Then look at your instructions - they tell you what to do:
1) To find out if a number is a MAGIC number or not add its digits.
2) Now add the digits of the sum obtained.
3) Repeat this process from (2) until you get a single digit number.
4) If you get 1 in the end the given number is a MAGIC number
5) It would appear this should be a method rather than direct in main.

Your code doesn't do that: It exit the loop as soon as the sum isn't one, regardless of the number of digits entered. So if I enter "11111111111112" it will process one single digit: "2" and exit the do loop. Think about how you detect you are out of digits ... it's pretty obvious!

I'd start by writing a "helper method" to take an integer parameter, and return the sum of it's digits.
Then call that in a loop until you have a single digit remaining.

Always sit down and think before you leap into code: it will save you a huge amount of wasted time. This may help you: How to Write Code to Solve a Problem, A Beginner's Guide[^]

Computer question from java

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