Sum of digits in C#

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

Answers:

You could do it arithmetically, without using a string:

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

Answers:

 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;
 }

Answers:

I use

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

It uses only 1 line of code.

Answers:

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.

Answers:

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.

Answers:

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

Answers:

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.

Answers:

I thought I'd just post this for completion's sake:

If you need a recursive sum of digits, e.g: 17463 -> 1 + 7 + 4 + 6 + 3 = 21 -> 2 + 1 = 3
then the best solution would be

int result = input % 9;
return (result == 0 && input > 0) ? 9 : result;

Answers:

The simplest and easiest way would be using loops to find sum of digits.

int sum = 0;
int n = 1234;

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

Answers:

int j, k = 1234;
for(j=0;j+=k%10,k/=10;);

Answers:

private static int getDigitSum(int ds)
{
    int dssum = 0;            
    while (ds > 0)
    {
        dssum += ds % 10;
        ds /= 10;
        if (dssum > 9)
        {                
            dssum -= 9;
        }
    }
    return dssum;
}

This is to provide the sum of digits between 0-9

Answers:

#include <stdio.h>

int main (void) {

    int sum = 0;
    int n;
    printf('Enter ir num ');
    scanf('%i', &n);

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

    printf('Sum of digits is %i
', sum);

    return 0;
}

Answers:

A while back, I had to find the digit sum of something. I used Muhammad Hasan Khan's code, however it kept returning the right number as a recurring decimal, i.e. when the digit sum was 4, i'd get 4.44444444444444 etc. Hence I edited it, getting the digit sum correct each time with this code:

 double a, n, sumD;
 for (n = a; n > 0; sumD += n % 10, n /= 10);
 int sumI = (int)Math.Floor(sumD);

where a is the number whose digit sum you want, n is a double used for this process, sumD is the digit sum in double and sumI is the digit sum in integer, so the correct digit sum.

Answers:

Surprised nobody considered the Substring method. Don't know whether its more efficient or not. For anyone who knows how to use this method, its quite intuitive for cases like this.

string number = '17463';
int sum = 0;
String singleDigit = '';
for (int i = 0; i < number.Length; i++)
{
singleDigit = number.Substring(i, 1);
sum = sum + int.Parse(singleDigit);
}
Console.WriteLine(sum);
Console.ReadLine();

Answers:

int n = 17463; int sum = 0;
for (int i = n; i > 0; i = i / 10)
{
sum = sum + i % 10;
}
Console.WriteLine(sum);
Console.ReadLine();

Answers:

static int SumOfDigits(int num)
{
    string stringNum = num.ToString();
    int sum = 0;
    for (int i = 0; i < stringNum.Length; i++)
    {
      sum+= int.Parse(Convert.ToString(stringNum[i]));

    }
    return sum;
}

Answers:

If one wants to perform specific operations like add odd numbers/even numbers only, add numbers with odd index/even index only, then following code suits best. In this example, I have added odd numbers from the input number.

using System;
                    
public class Program
{
    public static void Main()
    {
        Console.WriteLine("Please Input number");
        Console.WriteLine(GetSum(Console.ReadLine()));
    }
    
    public static int GetSum(string num){
        int summ = 0;
        for(int i=0; i < num.Length; i++){
            int currentNum;
            if(int.TryParse(num[i].ToString(),out currentNum)){
                 if(currentNum % 2 == 1){
                    summ += currentNum;
                }
            }
       } 
       return summ;
    }
}

Answers: