C Program for Sum the digits of a given number

Last Updated : 23 Jul, 2025

Given a number, find sum of its digits.
Example : 
 

Input : n = 687
Output : 21

Input : n = 12
Output : 3


1. Iterative: 

C 
// C program to compute sum of digits in 
// number.
# include<stdio.h>

/* Function to get sum of digits */
int getSum(int n)
{ 
   int sum = 0;
   while (n != 0)
   {
       sum = sum + n % 10;
       n = n/10;
   }
   return sum;
}

int main()
{
  int n = 687;
  printf(" %d ", getSum(n));
  return 0;
}

Time Complexity: O(log10n)

Auxiliary Space: O(1)

How to compute in single line?

c 
# include<stdio.h>
/* Function to get sum of digits */
int getSum(int n)
{
    int sum;

    /* Single line that calculates sum */
    for (sum=0; n > 0; sum+=n%10,n/=10);

    return sum;
}

int main()
{
  int n = 687;
  printf(" %d ", getSum(n));
  return 0;
}

2. Recursive

c 
int sumDigits(int no)
{
   return no == 0 ? 0 : no%10 + sumDigits(no/10) ;
}

int main(void)
{
    printf("%d", sumDigits(687));
    return 0;
}

Please refer complete article on Program for Sum the digits of a given number for more details!

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