/in/foo.cc: In function 'int main()':
/in/foo.cc:12:27: error: 'abs' was not declared in this scope
             if (n % abs (r)) ans[++ans[0]] = n % abs (r);
                           ^
/in/foo.cc:12:27: note: suggested alternative:
In file included from /in/foo.cc:2:0:
/usr/include/c++/6/cmath:103:5: note:   'std::abs'
     abs(_Tp __x)
     ^~~
/in/foo.cc:17:23: error: 'abs' was not declared in this scope
             if (abs (n) % abs (r)) {
                       ^
/in/foo.cc:17:23: note: suggested alternative:
In file included from /in/foo.cc:2:0:
/usr/include/c++/6/cmath:103:5: note:   'std::abs'
     abs(_Tp __x)
     ^~~