/in/foo.cc: In function 'int main()':
/in/foo.cc:14:10: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
    if (s % k == 0)
        ~~^~~
/in/foo.cc: In function 'long long int sum(long long int, long long int, long long int*)':
/in/foo.cc:28:9: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return s;
         ^