Newton Raphson solving x + log2(x) = 0

newton.cpp

#include <iostream>
#include <cmath>

// Newton Raphson solving x + log2(x) = 0
// https://en.wikipedia.org/wiki/Newton%27s_method
inline double func(double x) {
  return x + log2(x);
}

inline double derv(double x) {
  return 1 + log2(exp(1)) * 1/x;
}

inline double eval(double x, double y) {
  return y - func(x);
}

int main(int argc, char **argv) {
  const size_t iterations = 100;
  const double y = 0;
  const double thres = 0.0001;
  // initial guess
  double x_0 = 0.01;
  double x = x_0;
  for (size_t i = 0; i < iterations; i+=1) {
    x = x - func(x)/derv(x);
    if(eval(x, y) < thres) {
      break;
    }
    std::cout << "x: " << x << std::endl;
  }

  std::cout << "res: " << x << std::endl;
  return 0;
}