17. Extract the Nibble from an 8-bit Register

#include <stdio.h>

unsigned char extractNibble(unsigned char reg, int pos) {
    unsigned int output = 0;
    if(pos == 0) {
        return reg & 0x0F;
    }
    else if(pos == 1) {
        return (reg & 0xF0) >> 4;
    }
    
}

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

If pos is 0, we extract the lower nibble using bitwise AND. 

If pos is 1, we extract the higher nibble using bitwise AND and we right shift the output by 4 bits to bring it to the places of the lower nibble.