Complementary task for topic: 4

#include 

// Function to calculate the sum of digits
int sum_of_digits(int num) {
    int sum = 0;
    while (num != 0) {
        sum += num % 10;
        num /= 10;
    }
    return sum;
}

int main() {
    int num;
    printf("Enter a number to calculate the sum of its digits: ");
    scanf("%d", &num);

    int result = sum_of_digits(num);
    printf("Sum of digits of %d is %d.\n", num, result);

    return 0;
}

The sum_of_digits function takes an integer num as input and calculates the sum of its digits using a while loop. It extracts the last digit of num using the modulus operator (%) and adds it to the sum. Then, it removes the last digit from num by dividing it by 10 (num /= 10). The loop continues until num becomes 0. The function returns the final sum of digits.