# Finding sum of digits of a number until sum becomes single digit in C++

C++Server Side ProgrammingProgramming

In this tutorial, we are going to write a program that sums digits of the given number until it becomes a single digit. Let's see an example.

Input −4543

Output −7

Let's see the steps to solve the problem.

• Initialize a number.

• Initialize the sum to 0.

• Iterate until the sum is less than 9.

• Add each digit of the number to the sum using modulo operator

• Print the sum

## Example

Let's see the code.

Live Demo

#include <bits/stdc++.h>
using namespace std;
void findTheSingleDigit(int n) {
int sum = 0;
while(n > 0 || sum > 9) {
if(n == 0) {
n = sum;
sum = 0;
}
sum += n % 10;
n /= 10;
}
cout << sum << endl;
}
int main() {
int n = 4543;
findTheSingleDigit(n);
return 0;
}

## Output

you execute the above program, then you will get the following result.

7

We have another simple method to solve the problem. If the given number is divisible by 9, then the answer is 9. Else the number if n % 9.

## Example

Let's see the code.

Live Demo

#include <bits/stdc++.h>
using namespace std;
void findTheSingleDigit(int n) {
if (n == 0) {
cout << 0;
}
else if (n % 9 == 0) {
cout << 9 << endl;
}
else {
cout << n % 9 << endl;
}
}
int main() {
int n = 4543;
findTheSingleDigit(n);
return 0;
}

## Output

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

7

## Conclusion

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