Extract the Nibble from an 8-bit Register

Code

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

unsigned char extractNibble(unsigned char reg, int pos) {
    if (pos != 0 && pos != 1) return -1;
    uint8_t shift_val; 
    pos == 1 ? shift_val = 4 : shift_val = 0; 
    uint8_t mask = 0x0F; // mask to get all values in a nibble
    reg &= (mask << shift_val);
    return reg >> shift_val;;
}

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

Solving Approach