17. Extract the Nibble from an 8-bit Register

#include <stdio.h>

unsigned char extractNibble(unsigned char reg, int pos) {
    unsigned char mask = (1 << 4) - 1;
    if (pos == 1)
    {
        mask = ~mask; // flip to cover upper 4 bits
        return (reg & mask) >> 4; // make sure to shift back
    }

    return reg & mask;
}

int main() {
    unsigned char reg;
    int pos;
    scanf("%hhu %d", &reg, &pos);
    printf("%d", extractNibble(reg, pos));
    return 0;
}