/in/foo.cc: In member function 'Matrix Matrix::operator*(const Matrix&) const':
/in/foo.cc:10:37: error: 'memset' was not declared in this scope
   memset(res.mat, 0, sizeof(res.mat));
                                     ^
/in/foo.cc: In function 'Matrix pow_mod(Matrix, int)':
/in/foo.cc:21:36: error: 'memset' was not declared in this scope
  memset(res.mat, 0, sizeof(res.mat));
                                    ^