Sum digits of an integer

Sum digits of an integer is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

This task takes a Natural Number in a given Base and returns the sum of it digits:

1 sums to 1;

1234 sums to 10;

0xfe sums to 29;

0xf0e sums to 29.

C++

<lang cpp>#include <iostream>

1. include <cmath>

int SumDigits(const int digits, const int BASE = 10) {

       int sum = 0;
       int x = digits;
       for (int i = log(digits)/log(BASE); i>0; i--) {
               const int z = pow(BASE, i);
               const int t = x / z;
               sum += t;
               x -= t * z;
       }
       return x + sum;

}

int main() {

       std::cout << SumDigits(1) << ' '
                 << SumDigits(12345) << ' '
                 << SumDigits(123045) << ' '
                 << SumDigits(0xfe, 16) << ' '
                 << SumDigits(0xf0e, 16) << std::endl;
       return 0;

}</lang>

Output:

1 15 15 29 29

Erlang

<lang erlang> -module(sum_digits). -export([sum_digits/2, sum_digits/1]).

sum_digits(N) ->

   sum_digits(N,10).

sum_digits(N,B) ->

   sum_digits(N,B,0).

sum_digits(0,_,Acc) ->

   Acc;

sum_digits(N,B,Acc) when N < B ->

   Acc+N;

sum_digits(N,B,Acc) ->

   sum_digits(N div B, B, Acc + (N rem B)).

</lang>

Example usage:

2> sum_digits:sum_digits(1).
1
3> sum_digits:sum_digits(1234).
10
4> sum_digits:sum_digits(16#fe,16).
29
5> sum_digits:sum_digits(16#f0e,16).
29

J

<lang j>digsum=: 10&$: : (+/@(#.inv))</lang>

Example use:

<lang J> digsum 1234 10

  10 digsum 254

11

  16 digsum 254

29</lang>

Illustration of mechanics:

<lang j> 10 #. 1 2 3 4 1234

 10 #.inv 1234

1 2 3 4

 10 +/ 1 2 3 4

10

 10 +/@(#.inv) 1234

10</lang>

So #.inv gives us the digits, +/ gives us the sum, and @ glues them together with +/ being a "post processor" for #.inv or, as we say in the expression: (#.inv). We need the parenthesis or inv will try to look up the inverse of +/@#. and that's not well defined.

The rest of it is about using 10 as the default left argument when no left argument is defined. A J verb has a monadic definition (for use with one argument) and a dyadic definition (for use with two arguments) and : derives a new verb where the monadic definition is used from the verb on the left and the dyadic definition is used from the verb on the right. $: is a self reference to the top-level defined verb.

Full examples:

<lang j> digsum 1 1

  digsum 1234

10

  16 digsum 16bfe

29

  16 digsum 16bf0e

29</lang>

Note that J implements numeric types -- J tries to ensure that the semantics of numbers match their mathematical properties. So it doesn't matter how we originally obtained a number.

<lang j> 200+54 254

  254

254

  2.54e2

254

  16bfe

254</lang>

Java

<lang java>import java.math.BigInteger; public class SumDigits {

   public static int sumDigits(long num) {

return sumDigits(num, 10);

   }
   public static int sumDigits(long num, int base) {

String s = Long.toString(num, base); int result = 0; for (int i = 0; i < s.length(); i++) result += Character.digit(s.charAt(i), base); return result;

   }
   public static int sumDigits(BigInteger num) {

return sumDigits(num, 10);

   }
   public static int sumDigits(BigInteger num, int base) {

String s = num.toString(base); int result = 0; for (int i = 0; i < s.length(); i++) result += Character.digit(s.charAt(i), base); return result;

   }

   public static void main(String[] args) {

System.out.println(sumDigits(1)); System.out.println(sumDigits(12345)); System.out.println(sumDigits(123045)); System.out.println(sumDigits(0xfe, 16)); System.out.println(sumDigits(0xf0e, 16)); System.out.println(sumDigits(new BigInteger("12345678901234567890")));

   }

}</lang>

Output:

1
15
15
29
29
90

Ruby

<lang ruby>>> def sumDigits(num, base = 10) >> num.to_s(base).split(//).inject(0) {|z, x| z + x.to_i(base)} >> end => nil >> sumDigits(1) => 1 >> sumDigits(12345) => 15 >> sumDigits(123045) => 15 >> sumDigits(0xfe, 16) => 29 >> sumDigits(0xf0e, 16) => 29 </lang>