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Sum of digits in C

Sum of digits

Sum of digits C program to calculate the sum of digits of a number, we use modulus operator (%) to extract individual digits of a number and keep on adding them.

Sum of digits of a number in C

#include <stdio.h>

int main()
{
   int n, t, sum = 0, remainder;

   printf("Enter an integer\n");
   scanf("%d", &n);

   t = n;

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

   printf("Sum of digits of %d = %d\n", n, sum);

   return 0;
}

If you wish, you can modify the input variable (n) and without using an additional variable (t), but we don't recommend it.

Output of program:
Sum of digits C program output

For example, if the input is 98, the variable sum is 0 initially
98%10 = 8 (% is modulus operator, which gives us the remainder when 98 is divided by 10).
sum = sum + remainder
so sum = 8 now.
98/10 = 9 because in C language, whenever we divide an integer by another one, we get an integer.
9%10 = 9
sum = 8 (previous value) + 9
sum = 17
9/10 = 0.
So finally, n = 0, the loop ends; we get the required sum.

Download Add digits program.

C program to find sum of digits using for loop

#include <stdio.h>

int main()
{
   int n, sum = 0, r;

   printf("Enter a number\n");

   for (scanf("%d", &n); n != 0; n = n/10) {
      r = n % 10;
      sum = sum + r;
   }

   printf("Sum of digits of a number = %d\n", sum);

   return 0;
}

Calculate sum of digits in C without modulus operator

C program to find the sum of digit(s) of an integer that does not use modulus operator. Our program uses a character array (string) for storing an integer. We convert its every character into an integer and add all these integers.

#include <stdio.h>
 
int main()
{
   int c, sum, t;
   char n[1000];
   
   printf("Input an integer\n");
   scanf("%s", n);
 
   sum = c = 0;
   
   while (n[c] != '\0') {
      t   = n[c] - '0'; // Converting character to integer
      sum = sum + t;
      c++;
   }
 
   printf("Sum of digits of %s = %d\n", n, sum);
 
   return 0;
}

An advantage of this method is that the input integer can be huge, which we can't store in an int or a long long data type variable. See the example below.

Output of program:

Input an integer
9876543210
Sum of digits of 9876543210 = 45

C program to find sum of digits of a number using recursion

#include <stdio.h>

int add_digits(int);

int main()
{
  int n, result;

  scanf("%d", &n);

  result = add_digits(n);

  printf("%d\n", result);

  return 0;
}

int add_digits(int n) {
  if (n == 0)  // Base case
    return 0;

  return (n%10 + add_digits(n/10));
}