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.
int n, sum = 0, remainder;
printf("Enter an integer");
while(n != 0)
remainder = n % 10;
sum = sum + remainder;
n = n / 10;
printf("Sum of digits of entered number = %dn",sum);