1 #include<stdio.h>
  2 int main()
  3 {
  4    int a=0xaa;
  5    a|=0x55;
  6    printf("a  is  %x\n",a);
  7    a=0xaa;
  8    a&=~(0xa);
  9    printf("a  is  %x\n",a);
 10 }

注意写法
a|=0x55;
and
a&=~(0xa);