How I would do FizzBuzz

#include <cstdint>
#include <cstdio>

//
// only accurate for n up to 99999999
//
// only accurate on little-endian machines
//
void fb(int64_t n, char *out) {
  *(int64_t *)out =
    (n * 0xaaaaaaaaaaaaaaab < 0x5555555555555556) * 0x000000007a7a6946 ^
    (n * 0xcccccccccccccccd < 0x3333333333333334) * 0x000000007a7a7542 ^
    (n * 0xeeeeeeeeeeeeeeef < 0x1111111111111112) * 0x7a7a75427a7a7542;
  if (*out == 0) {
    sprintf(out, "%lld", n);
  }
}

int main(int argc, char **argv) {
  char s[9] = {0};
  for (int i = 1; i <= 100; i++) {
    fb(i, s);
    printf("%s\n", s);
  }
  return 0;
}

See Database of 2-adic Integers

Inspired by https://gynvael.coldwind.pl/n/c_cpp_number_to_binary_string_01011010

Hint: “FizzBuzz” has 8 letters