imaginary
Defined in header <complex.h>


#define imaginary _Imaginary 
(since C99)  
This macro expands to the keyword _Imaginary.
This is a convenience macro that makes it possible to use float imaginary, double imaginary, and long double imaginary as an alternative way to write the three pure imaginary C types float _Imaginary, double _Imaginary, and long double _Imaginary
As with any pure imaginary number support in C, this macro is only defined if the imaginary numbers are supported.
A compiler that defines __STDC_IEC_559_COMPLEX__ is not required to support imaginary numbers. POSIX recommends checking if the macro _Imaginary_I is defined to identify imaginary number support. 
(since C99) (until C11) 
Imaginary numbers are supported if __STDC_IEC_559_COMPLEX__ is defined. 
(since C11) 
Notes
Programs are allowed to undefine and perhaps redefine the imaginary macro.
Example
Output:
z = 1.0+2.0i
References
 C11 standard (ISO/IEC 9899:2011):
 7.3.1/5 imaginary (p: 188)
 G.6/1 imaginary (p: 537)
 C99 standard (ISO/IEC 9899:1999):
 7.3.1/3 imaginary (p: 170)
 G.6/1 imaginary (p: 472)
See also
(C99) 
complex type macro (macro constant) 