Sum of digits of a user entered number in C program

We can ask the user to enter a number. We will use one while loop to find out each digit present in the number.

Each step of the loop will collect one digit ( right most ) by dividing the number with 10 and storing the reminder. Each time ( loop ) reminder we will add up by storing in a variable sum.

#include <stdio.h>

int main()
{
 int n, sum = 0, remainder;
 
   printf("Enter an integer");
   scanf("%d",&n);
 
   while(n != 0)
   {
      remainder = n % 10;
      sum = sum + remainder;
      n = n / 10;
   }
 
   printf("Sum of digits of entered number = %dn",sum);
 
return 0;
}

Example: Recursive Function to Sum Digits

Shows how recursion can be used to sum digits.

#include <stdio.h>

int sumDigits(int num) {
    if (num == 0)
        return 0;
    return (num % 10) + sumDigits(num / 10);
}

int main() {
    int number = 12345;
    printf("Sum of digits: %d\n", sumDigits(number));
    return 0;
}

Output

Sum of digits: 15

Example: Sum of Digits for an Array of Numbers

Demonstrates how to compute the sum of digits for multiple numbers in an array.

#include <stdio.h>

int sumDigits(int num) {
    int sum = 0;
    while (num != 0) {
        sum += num % 10;
        num /= 10;
    }
    return sum;
}

int main() {
    int numbers[] = {123, 456, 789, 12};
    int size = sizeof(numbers) / sizeof(numbers[0]);

    for (int i = 0; i < size; i++) {
        printf("Sum of digits of %d is: %d\n", numbers[i], sumDigits(numbers[i]));
    }

    return 0;
}

Output

Sum of digits of 123 is: 6
Sum of digits of 456 is: 15
Sum of digits of 789 is: 24
Sum of digits of 12 is: 3

Example: Sum of Digits Handling Negative Numbers

Ensures negative numbers are handled correctly by using abs().

#include <stdio.h>
#include <stdlib.h>

int sumDigits(int num) {
    num = abs(num);  // Handle negative numbers by taking absolute value
    int sum = 0;
    while (num != 0) {
        sum += num % 10;
        num /= 10;
    }
    return sum;
}

int main() {
    int number = -12345;
    printf("Sum of digits of %d is: %d\n", number, sumDigits(number));
    return 0;
}

Output

Sum of digits of -12345 is: 15

Sample scripts in C Grade Mark C- Tutorials

Sum of digits of a number

Example: Recursive Function to Sum Digits

Example: Sum of Digits for an Array of Numbers

Example: Sum of Digits Handling Negative Numbers