# imaginary

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< c‎ | numeric‎ | complex

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

Run this code

    #include <stdio.h>
    #include <complex.h>

    int main(void)
    {
        double imaginary i = 2.0*I; // pure imaginary
        double f = 1.0; // pure real
        double complex z = f + i; // complex number
        printf("z = %.1f%+.1fi\n", creal(z), cimag(z));
    }

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

complex (C99) | complex type macro (macro constant)

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