Check if a large number is divisible by 2, 3 and 5 or not in C++

Here we will see how to check a number is divisible by 2, 3 and 5 or not. In this case the number is very large number. So we put the number as string.

A number will be divisible by 2, 3 and 5 if that number is divisible by LCM of 2,3 and 5. So the LCM of 2, 3, 5 is 30. We have to check the number is divisible by 30 or not. A number is divisible by 30 when it is divisible by 10 (last digit is 0) and divisible by 3 (sum of all digits is divisible by 3)

Example

#include <bits/stdc++.h>
using namespace std;
bool isDiv30(string num){
   int n = num.length();
   if(num[n - 1] != '0')
      return false;
      long sum = accumulate(begin(num), end(num), 0) - '0' * n;
   if(sum % 3 == 0)
      return true;
   return false;
}
int main() {
   string num = "353730746028908374890";
   if(isDiv30(num)){
      cout << "Divisible";
   } else {
      cout << "Not Divisible";
   }
}

Output

Divisible