C - finding cube root of a negative number with pow function

Question

In real world cube root for a negative number should exist: cuberoot(-1)=-1, that means (-1)*(-1)*(-1)=-1 or cuberoot(-27)=-3, that me

Answer 1

As Stephen Canon answered, to correct function to use in this case is cbrt(). If you don't know the exponent beforehand, you can look into the cpow() function.

#include 
#include 
#include 

int main(void)
{
    printf("cube root cbrt: %g\n", cbrt(-27.));
    printf("cube root pow: %g\n", pow(-27., 1./3.));
    double complex a, b, c;
    a = -27.;
    b = 1. / 3;
    c = cpow(a, b);
    printf("cube root cpow: (%g, %g), abs: %g\n", creal(c), cimag(c), cabs(c));
    return 0;
}

prints

cube root cbrt: -3
cube root pow: -nan
cube root cpow: (1.5, 2.59808), abs: 3

Keep in mind the definition of the complex power: cpow(a, b) = cexp(b* clog(a)).