C++ Random generator demo

#include <cstdio>
#include <ctime>
#include <random>

static std::random_device rd;
std::mt19937 gen_eng(rd.entropy() ? rd() : (unsigned long)(std::time(nullptr)));
//Or just "std::mt19937 generator(SOME_CONST);" for repeated sequence. Try it!

double genAlpha() {
  static std::uniform_real_distribution<double> unif_real_01(0.0, 1.0);
  return unif_real_01(gen_eng);
}

int main() {
  printf("%lf\n", genAlpha());
  printf("%lf\n", genAlpha());
  printf("%lf\n", genAlpha());
  printf("%lf\n", genAlpha());

  printf("\nMmm... Dice throwing:\n");
  int dice_result = 6 * genAlpha() + 1;
  printf("%d\n", dice_result);

  printf("\nADVANCED\nWe can get another distributions:\n");
  printf("1) Dice (\"right\" way):\n");

  std::uniform_int_distribution<int> unif_int_16(1, 6);

  printf("%d\n", unif_int_16(gen_eng));
  printf("%d\n", unif_int_16(gen_eng) + unif_int_16(gen_eng) + unif_int_16(gen_eng));
  printf("2) Normal:\n");

  static std::normal_distribution<double> std_norm_dist(0, 1);

  printf("%lf\n", std_norm_dist(gen_eng));
  printf("%lf\n", std_norm_dist(gen_eng));
  printf("%lf\n", std_norm_dist(gen_eng));
  printf("%lf\n", std_norm_dist(gen_eng));

  return 0;
}