How to check for division by 7 for big number in C++?

Question

I have to check, if given number is divisible by 7, which is usualy done just by doing something like n % 7 == 0, but the problem is, that given number can have

Answer 1

At first Take That Big Number in string And then sum every digit of string. at last check if(sum%7==0)

Code:

#include 
using namespace std;
int main()
{
    long long int n,i,j,sum,k;
    sum=0;
    string s;
    cin>>s;
    for(i=0;i