/in/foo.cc: In function 'bool is_perfect_square(int)':
/in/foo.cc:11:27: error: 'sqrt' was not declared in this scope
     double s = fmod(sqrt(x), 1.0);
                           ^
/in/foo.cc:11:33: error: 'fmod' was not declared in this scope
     double s = fmod(sqrt(x), 1.0);
                                 ^