/in/foo.cc: In function 'int main()':
/in/foo.cc:15:39: error: 'sqrt' was not declared in this scope
   int j = (int)(ceil(sqrt(2 * i + 2.25) + 0.5) - 0.999) - 1;
                                       ^
/in/foo.cc:15:46: error: 'ceil' was not declared in this scope
   int j = (int)(ceil(sqrt(2 * i + 2.25) + 0.5) - 0.999) - 1;
                                              ^