Check if a large number is divisible by 9 or not in C++

Here we will see how to check a number is divisible by 9 or not. In this case the number is very large number. So we put the number as string.

A number will be divisible by 9, if the sum of digits is divisible by 9.

Example

#include <bits/stdc++.h>
using namespace std;
bool isDiv3(string num){
   int n = num.length();
   long sum = accumulate(begin(num), end(num), 0) - '0' * n;
   if(sum % 9 == 0)
      return true;
      return false;
}
int main() {
   string num = "630720";
   if(isDiv3(num)){
      cout << "Divisible";
   } else {
      cout << "Not Divisible";
   }
}

Output

Divisible