std::complex::imag
From cppreference.com
                    
                                        
                    
                    
                                                            
                    | T imag() const; | (1) | |
| void imag( T value ); | (2) | |
Accesses the imaginary part of the complex number.
1) Returns the imaginary part.
2) Sets the real imaginary to value.
[edit] Parameters
| value | - | the value to set the imaginary part to | 
[edit] See also
| accesses the real part of the complex number (public member function) | |