This problem can be solved using two different approach:

• using iterative approach and

• recursive approach

For example, if a number 1234 is given as input then sum of its digit is 1 + 2 + 3 + 4 = 10.

1. Iterative Approach

#include<stdio.h>

int sumOfDigits(int num){

int sum = 0;

while(num>0){

sum = sum + num%10;

num = num/10;

}

return sum;

}

int main(){

int num;

printf("Enter a number::");

scanf("%d",&num);

int sum = sumOfDigits(num);

printf("The sum of digits of %d is %d",num,sum);

return 0;

}

2. The Recursive Approach

#include<stdio.h>

int sumOfDigits(int num){

if(num>0){

return num%10 + sumOfDigits(num/10);

}

}

int main(){

int num;

printf("Enter a number::");

scanf("%d",&num);

int sum = sumOfDigits(num);

printf("The sum of digits of %d is %d",num,sum);

return 0;

}