====== cacos ======
<code c>
double complex cacos(double complex z);
</code>

==== description of cacos ====
compute the complex arc cosine of z\\
with branch cuts outside the interval (from -1 to +1) along the real axis. 


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

int main( void )
{

   long double complex zlong=4.2 + I*2.34;
   double complex zdouble=(double complex)zlong;

   double result;

   result = cacos(zdouble);
   printf("cacos(%f + I*%f) = %f\n", creal(zdouble), cimag(zdouble), result);
   return 0;
}
</code>

===== output of cacos c example =====
    cacos(4.200000 + I*2.340000) = 0.517664