Here's a fancier, slightly less-magic, version. How to compile is left as an exercise for the reader (hint: Haswell or newer, requires BMI2 instruction set):

    void toBinary(uint8_t byte) {
        uint64_t zeroes = *(uint64_t *)"00000000";
        uint64_t resultStr =
            zeroes | __builtin_bswap64(_pdep_u64(byte, 0x0101010101010101ULL));
    
        printf("hello: %.*s\n", 8, (char *)&resultStr);
    }