17. Extract the Nibble from an 8-bit Register

#include <stdio.h>

unsigned char extractNibble(unsigned char reg, int pos) {
    // Write your code here
    switch (pos) {
    case 0:
        return (0x0F & reg);

    case 1:
    default:
        return (reg >> 4);
    }
}

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

for the lower nibble you clear the top nibble by "bitwise and" with 0x0F

to get the upper nibble, shift right four bits