/in/foo.cc: In function 'int main()':
/in/foo.cc:15:10: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
    if (s % k == 0)
        ~~^~~
/in/foo.cc: In function 'long long int sum(int, int, int*)':
/in/foo.cc:29:9: warning: 's' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return s;
         ^