Count Set Bits in an 8-bit Register

#include <stdio.h>
#include <stdint.h>

uint8_t count_set_bits(uint8_t reg) {
    int set_bits = 0;
    for (int i = 0; i < sizeof(reg)*8; i++){
        set_bits += ((reg >> i) & 0x01);
    }
    return set_bits;
}

int main() {
    uint8_t reg;
    scanf("%hhu", &reg);
    printf("%u", count_set_bits(reg));
    return 0;
}