cproj

double complex cproj(double complex z);

calculate the projection

#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 = cproj(zdouble);
   printf("cproj(%f + I*%f) = %f\n", creal(zdouble), cimag(zdouble), result);
   return 0;
}

  cproj(4.200000 + I*2.340000) = 4.200000