Sum of digits in C#

Question

What's the fastest and easiest to read implementation of calculating the sum of digits?

I.e. Given the number: 17463 = 1 + 7 + 4 + 6 + 3 = 21

Answer 1

You could do it arithmetically, without using a string:

sum = 0;
while (n != 0) {
    sum += n % 10;
    n /= 10;
}

Answer 2

 public static int SumDigits(int value)
 {
     int sum = 0;
     while (value != 0)
     {
         int rem;
         value = Math.DivRem(value, 10, out rem);
         sum += rem;
     }
     return sum;
 }

Answer 3

I use

int result = 17463.ToString().Sum(c => c - '0');

It uses only 1 line of code.

Answer 4

I like the chaowman's response, but would do one change

int result = 17463.ToString().Sum(c => Convert.ToInt32(c));

I'm not even sure the c - '0', syntax would work? (substracting two characters should give a character as a result I think?)

I think it's the most readable version (using of the word sum in combination with the lambda expression showing that you'll do it for every char). But indeed, I don't think it will be the fastest.

Answer 5

For integer numbers, Greg Hewgill has most of the answer, but forgets to account for the n < 0. The sum of the digits of -1234 should still be 10, not -10.

n = Math.Abs(n);
sum = 0;
while (n != 0) {
    sum += n % 10;
    n /= 10;
}

It the number is a floating point number, a different approach should be taken, and chaowman's solution will completely fail when it hits the decimal point.

Answer 6

int num = 12346;
int sum = 0;
for (int n = num; n > 0; sum += n % 10, n /= 10) ;

Answer 7

I would suggest that the easiest to read implementation would be something like:

public int sum(int number)
{
    int ret = 0;
    foreach (char c in Math.Abs(number).ToString())
        ret += c - '0';
    return ret;
}

This works, and is quite easy to read. BTW: Convert.ToInt32('3') gives 51, not 3. Convert.ToInt32('3' - '0') gives 3.

I would assume that the fastest implementation is Greg Hewgill's arithmetric solution.