pack unpack bits

#include <stdio.h>

void printBits(unsigned x) {
  for (int i = sizeof(x) * 8 - 1; i >= 0; i--) {
    printf("%d", 1 & (x >> i));
    if (i % 4 == 0) {
      putchar(' ');
    }
  }
  puts("");
}

unsigned char pack(unsigned a, unsigned b) {
  unsigned char r = 0;
  r |= a;
  r |= (b << 4);
  return r;
}

void unpack(unsigned char ch) {
  unsigned mask = (1 << 4) - 1;
  unsigned fi = mask & ch;
  unsigned se = mask & (ch >> 4);
  printf("%u\n%u\n", fi, se);
}

int main(void) {
  unsigned a, b;
  scanf("%u", &a);
  scanf("%u", &b);

  printBits(a);
  printBits(b);

  unsigned char ch = pack(a, b);
  printBits(ch);
  unpack(ch);

  return 0;
}