bitwise substract

#include <stdio.h>

unsigned substract(unsigned a, unsigned b) {
  while (b) {
    unsigned borrow = ~a & b;
    unsigned diff = a ^ b;
    borrow <<= 1;
    a = diff;
    b = borrow;
  }
  return a;
}

int main(void) {
  unsigned a, b, diff;
  scanf("%u", &a);
  scanf("%u", &b);
  diff = substract(a, b);
  printf("%u-%u=%u\n", a, b, diff);
  return 0;
}