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ISO C99 introduces support for complex numbers in C. This is done
with a new type qualifier,
complex. It is a keyword if and only
if `complex.h' has been included. There are three complex types,
corresponding to the three real types:
double complex, and
long double complex.
To construct complex numbers you need a way to indicate the imaginary part of a number. There is no standard notation for an imaginary floating point constant. Instead, `complex.h' defines two macros that can be used to create complex numbers.
_Complex_Igives a complex number whose value is purely imaginary. You can use this to construct complex constants:
3.0 + 4.0i =
_Complex_I * _Complex_I has the value
the type of that value is
_Complex_I is a bit of a mouthful. `complex.h' also defines
a shorter name for the same constant.
_Complex_I. Most of the time it is preferable. However, it causes problems if you want to use the identifier
Ifor something else. You can safely write
#include <complex.h> #undef I
if you need
I for your own purposes. (In that case we recommend
you also define some other short name for
_Complex_I, such as
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