#include <complex.h>

       Complex  numbers  are  numbers of the form z = a+b*i, where a and b are
       real numbers and i = sqrt(-1), so that i*i = -1.
       There are other ways to represent that number.  The pair (a,b) of  real
       numbers  may be viewed as a point in the plane, given by X- and Y-coor-
       dinates.  This same point may also be described by giving the  pair  of
       real  numbers (r,phi), where r is the distance to the origin O, and phi
       the angle between the X-axis and the line Oz.  Now z =  r*exp(i*phi)  =

       The basic operations are defined on z = a+b*i and w = c+d*i as:

       addition: z+w = (a+c) + (b+d)*i

       multiplication: z*w = (a*c - b*d) + (a*d + b*c)*i

       division: z/w = ((a*c + b*d)/(c*c + d*d)) + ((b*c - a*d)/(c*c + d*d))*i

       Nearly  all math function have a complex counterpart but there are some
       complex-only functions.

       Your C-compiler can work with complex numbers if it  supports  the  C99
       standard.  Link with -lm.  The imaginary unit is represented by I.

       /* check that exp(i * pi) == -1 */
       #include <math.h>        /* for atan */
       #include <stdio.h>
       #include <complex.h>

           double pi = 4 * atan(1.0);
           double complex z = cexp(I * pi);
           printf("%f + %f * i\n", creal(z), cimag(z));

       cabs(3),  cacos(3),  cacosh(3), carg(3), casin(3), casinh(3), catan(3),
       catanh(3), ccos(3), ccosh(3),  cerf(3),  cexp(3),  cexp2(3),  cimag(3),
       clog(3),  clog10(3),  clog2(3),  conj(3),  cpow(3), cproj(3), creal(3),
       csin(3), csinh(3), csqrt(3), ctan(3), ctanh(3)

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