# Sum of digits in C

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

## C programming code

1. #include <stdio.h>
2.
3. int main()
4. {
5.    int n, t, sum = 0, remainder;
6.
7.    printf("Enter an integer\n");
8.    scanf("%d", &n);
9.
10.    t = n;
11.
12.    while (t != 0)
13.    {
14.       remainder = t % 10;
15.       sum       = sum + remainder;
16.       t         = t / 10;
17.    }
18.
19.    printf("Sum of digits of %d = %d\n", n, sum);
20.
21.    return 0;
22. }

If you wish you can modify the input variable (n) and without using an additional variable (t) but it isn't recommended.

Output of program:

For example, if the input is 98, the variable sum is 0 initially
98%10 = 8 (% is modulus operator which gives us 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 an another integer 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.

## Calculate sum of digits in C without modulus operator

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

1. #include <stdio.h>
2.
3. int main()
4. {
5.    int c, sum, t;
6.    char n[1000];
7.
8.    printf("Input an integer\n");
9.    scanf("%s", n);
10.
11.    sum = c = 0;
12.
13.    while (n[c] != '\0') {
14.       t   = n[c] - '0'; // Converting character to integer
15.       sum = sum + t;
16.       c++;
17.    }
18.
19.    printf("Sum of digits of %s = %d\n", n, sum);
20.
21.    return 0;
22. }

An advantage of this method is that input integer can be very large which can't be stored in an int or a long long variable, see an example below.

Output of program:

1. Input an integer
2. 123456789123456789123456789
3. Sum of digits of 123456789123456789123456789 = 135

## Sum of digits of a number C program using recursion

1. #include <stdio.h>
2.
4.
5. int main()
6. {
7.   int n, result;
8.
9.   scanf("%d", &n);
10.
12.
13.   printf("%d\n", result);
14.
15.   return 0;
16. }
17.