Find Sum of Digits of a Number using Recursion in C, C++

Write a program to find sum of digits of a number using recursion in C, C++. This is a simple question to understand and implement recursion concept. In this program we take a number from user then add the digits of a number recursively and finally return the result.

I already discussed the iterative version of this program. Program to calculate the sum of digits of a number.

In this program we used recursion to add digits of a number. In programming recursion and iteration are two very important concepts. Read the difference between recursion and iteration.

Programming interview questions

Objective Question on Recursion

Find Sum of Digits of a Number using Recursion in C

#include <stdio.h>

int addDigit(int num) {

   if (num <= 0) {
  
     return 0;
  
   } 
 
   return ( num % 10) + addDigit( num / 10);
}

int main(void) {
 
  int n, result;
 
  printf ("Enter a number : \n");
  scanf ("%d", &n);
 
  result = addDigit(n);
 
  printf("Sum of digits of a number is %d",result);
 
  return 0;
}

Output -

Enter a number :   345

Sum of digits of a number is  :  12


Explanation

Suppose you have entered a number 345. Let's see how this program work.

Step 1  -  5 + addDigit (34)

Step 2 -  5 +  4 + addDigit (3)

Step 3 -  5  +  4 +  3 + addDigit (0)

Step 4 -  5  +  4  + 3  + 0

Now final result is returned.

Find Sum of Digits of a Number using Recursion in C++

#include <iostream>
using namespace std;

int addDigit(int num) {

   if (num <= 0) {
  
      return 0;
  
    } 
 
    return ( num % 10) + addDigit( num / 10);
}

int main() {
 
   int n, result;
 
   cout << "Enter a number \n";
   cin >> n;
 
   result = addDigit(n);
 
   cout << "Sum of digits of a number is " << result;
 
   return 0;
}