We use **`_Complex`** to declare a complex number in C. 

It is an expansion of the `complex` macro in `<complex.h>`

A complex number is written as the sum of one real number and one real number multiplied by the imaginary unit, I.

# _Complex types

The following are the three `_Complex` types:

1. `float _Complex`
2. `double _Complex`
3. `long double _Complex`

>By including the `<complex.h>` header, we can replace the `_Complex` keyword with `complex` and have the same effect. 


#include <complex.h>
#include <stdio.h>
int main(void)
{
    //declaring a complex number using complex
    double complex z1 = 1 + 2*I;

    //Arithmetic operation
    z1 = 2 * z1;

    //Printing correct to 1dp
    printf("2 * (1.0+2.0i) = %.1f%+.1fi\n", creal(z1), cimag(z1));

    //declaring a complex number using _Complex
    double _Complex z2 = 3 + 4*I;

    //Arithmetic operation
    z2 = 1 / z2;

    //Printing correct to 1dp
    printf("1 / (3.0+4.0i) = %.1f%+.1fi\n", creal(z2), cimag(z2));
}

In the above example, we declare two complex numbers. 

To define the imaginary part of the number, we multiply a real number with I.

Next, we perform a mathematical operation on the complex numbers.

Finally, the results are printed.

>`creal()` and `cimag()` are defined in the `<complex.h>` header. We use these to extract the real and imaginary parts of a complex number, respectively. 

What is the _Complex keyword in C?

_Complex in C declares complex numbers, equivalent to the `complex` macro in `<complex.h>`. Types include `float _Complex`, `double _Complex`, and `long double _Complex`.

What is the _Complex keyword in C?

_Complex types

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