| Types and the imaginary constant | |||||||||||||||||||||||||||||||
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| Manipulation | |||||||||||||||||||||||||||||||
| Power and exponential functions | |||||||||||||||||||||||||||||||
| Trigonometric functions | |||||||||||||||||||||||||||||||
| Hyperbolic functions | |||||||||||||||||||||||||||||||
Defined in header <complex.h> | ||
#define I /* unspecified */ | (since C99) | |
TheI macro expands to either_Complex_I or_Imaginary_I. If the implementation does not support imaginary types, then the macro always expands to_Complex_I.
A program may undefine and perhaps then redefine the macroI.
Contents |
The macro is not namedi, which is the name of the imaginary unit in mathematics, because the namei was already used in many C programs, e.g. as a loop counter variable.
The macroI is often used to form complex numbers, with expressions such asx+ y*I. IfI is defined as_Complex_I, then such expression may create a value with imaginary component+0.0 even wheny is-0.0, which is significant for complex number functions with branch cuts. The macroCMPLX provides a way to construct a complex number precisely.
GCC provides a non-portable extension that allows imaginary constants to be specified with the suffixi on integer literals:1.0fi,1.0i, and1.0li are imaginary units in GNU C. A similar approach is part of standard C++ as of C++14 (1.0if,1.0i, and1.0il are the imaginary units in C++)
#include <stdio.h>#include <complex.h> int main(void){printf("I = %.1f%+.1fi\n",creal(I),cimag(I)); doublecomplex z1= I* I;// imaginary unit squaredprintf("I * I = %.1f%+.1fi\n",creal(z1),cimag(z1)); doublecomplex z=1.0+2.0*I;// usual way to form a complex number pre-C11printf("z = %.1f%+.1fi\n",creal(z),cimag(z));}
Output:
I = 0.0+1.0iI * I = -1.0+0.0iz = 1.0+2.0i
(C99) | the imaginary unit constant i (macro constant)[edit] |
(C99) | the complex unit constant i (macro constant)[edit] |
(C11)(C11)(C11) | constructs a complex number from real and imaginary parts (function macro)[edit] |
C++ documentation foroperator""i | |
