Find a number x such that sum of x and its digits is equal to given n in C++

Here we will see one problem, where we take a number n, we have to find another value say x, such that x + digit sum of x is same as the given number n. Suppose the value of n is 21. This program will return a number x = 15, as 15 + digit sum of 15, i.e. 15 + 1 + 5 = 21 = n.

To solve this problem, we have to follow simple approach. We will iterate through 1 to n, in each iteration, we will see if the sum of the number and its digit sum is same as the number, then stop, otherwise continue.


 Live Demo

using namespace std;
int getDigitSum(int n) {
   int sum = 0;
   while (n) {
      sum += n % 10;
      n /= 10;
   return sum;
int getNumber(int n) {
   for (int i = 0; i <= n; i++)
      if (i + getDigitSum(i) == n)
         return i;
         return -1;
int main() {
   int n = 21;
   cout << "The value of x is: " << getNumber(n);


The value of x is: 15

Updated on: 24-Oct-2019


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