complex in C

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. There are three complex types, corresponding to the three real types: float complex, double complex, and long double complex.
```
#include <complex.h>    /* Standard Library of Complex Numbers */

int main() {
    double complex z1 = 1.0 + 3.0 * I;
    double complex z2 = 1.0 - 4.0 * I;
}
```