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Sum of digits of a number

Abstract

Java program, asking user for a positive integer and calculating sum of its digits then.

Source code

SumOfDigits.java

import java.util.Scanner;

 

public class SumOfDigits {

      public static void main(String[] args) {

            Scanner in = new Scanner(System.in);

            int n;

            System.out.print("Enter a positive integer: ");

            n = in.nextInt();

            if (n <= 0)

                  System.out.println("Integer you've entered is nonpositive.");

            else {

                  int sum = 0;

                  // algorithm step by step

                  // base:  sum = 0, n = 123

                  // step1: n % 10 = 3, n / 10 = 12

                  //        sum = 3, n = 12

                  // step2: n % 10 = 2, n / 10 = 1

                  //        sum = 5, n = 1

                  // step3: n % 10 = 1, n / 10 = 0

                  //        sum = 6, n = 0

                  // stop:  (n != 0) is false

                  while (n != 0) {

                        // add last digit to the sum

                        sum += n % 10;

                        // cut last digit

                        n /= 10;

                  }

                  System.out.println("Sum of digits: " + sum);

            }

      }

}

Download SumOfDigits.java

Sample run

Enter a positive integer: 123

Sum of digits: 6