Digital Root (repeated digital sum) of the given large integer in C++ Program

In this tutorial, we are going to learn how to find the digital root of a given number.

The digital root is the sum of a number of digits (until the sum of the digits becomes a single digit).

We are given an integer in string format. And we have to find the sum of the digits repeatedly until the sum becomes a single digit.

Let's see the steps to solve the problem.

  • Initialize an integer in the string format.

  • Iterate through the number and add each digit to the sum variable.

  • If the sum is 0, then print 0.

  • Else if the sum is divisible by 9, then the answer is 9.

  • Else the answer is sum modulo 9.


Let's see the code.

 Live Demo

using namespace std;
int digitalRoot(string n) {
   int digitsSum = 0;
   for (int i = 0; i < n.length(); i++) {
      digitsSum += n[i] - '0';
   if (digitsSum == 0) {
      return 0;
   return digitsSum % 9 == 0 ? 9 : digitsSum % 9;
int main() {
   string n = "12345";
   cout << digitalRoot(n) << endl;
   return 0;


If you run the above code, then you will get the following result.



If you have any queries in the tutorial, mention them in the comment section.

Updated on: 27-Jan-2021


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