Here’s my answer to the supposedly toughest question in Chapter 2 of the text book:

// Write a program that reads in an integer between 0 and 1000 and adds all the
// digits in the integer. For example, 932 returns 14

import java.util.Scanner;

public class IntAdder{
    public static void main(String[] args){
        int input=0;
        int result=0;
        Scanner sc = new Scanner(System.in);

        System.out.print("Enter integer: ");
        input = sc.nextInt();

        while(input!=0){
            result += input%10;
            input /= 10;
        }

        System.out.println("Sum is " + result);

    }

}

Input : 123
Output: 6