[c/c++] programming之路（30）、位运算（一）

一、取反　　~

#include<stdio.h>
#include<stdlib.h>

void main(){
    unsigned char ch=15;    //0000 1111     char的单位是字节，1B=8bit，所以是8位
    unsigned char fch=~ch;    //1111 0000     取反      
    unsigned char ffch=~fch;//0000 1111     

    printf("%d,%d,%d\n",ch,fch,ffch);
    system("pause");
}

注意：取反运算符不改变操作数的值，赋值运算符才会改变。

二、与运算　　&

#include<stdio.h>
#include<stdlib.h>

//位与    1,1->1    01,10,00->0
//1&0=0 , 0&0=0    ->清零
//1&1=1 ，0&1=0 ->保留某些位不变 

void main0(){
    unsigned char ch1=3;    //0000 0011     
    unsigned char ch2=240;    //1111 0000         
    unsigned char ch3=255;    //1111 1111

    printf("%d\n",ch1&ch2); //0000 0000  0
    printf("%d\n",ch1&ch3); //0000 0011  3
    printf("%d\n",ch2&ch3); //1111 0000  240
    system("pause");
}

//位与实现按位清零
void main1(){
    unsigned char ch1=255;    //1111 1111     
    unsigned char ch2=15;    //0000 1111         
    unsigned char ch3=240;    //1111 0000         
    
    printf("%d\n",ch1&ch2); //清零高四位
    printf("%d\n",ch1&ch3); //清零低四位
    printf("%d\n",ch1&0);    //全部清零
    system("pause");
}

//位与实现取出指定位
void main(){
    unsigned char ch=169;    //1010 1001
    unsigned char ch1=60;    //0011 1100     
                            //0010 1000        40
    
    printf("%d\n",ch&ch1); //取出中间四位
    system("pause");
}

三、或运算　　|

#include<stdio.h>
#include<stdlib.h>

//位或运算    1|1=1    1|0=1    0|1=1    0|0=0
void main0(){
    unsigned char ch=169;    //1010 1001
    unsigned char ch1=240;    //1111 0000     
                            //1111 1001        249
    printf("%d\n",ch|ch1); 
    system("pause");
}

//位或运算符可以让某些位变成1    1|0 = 1|1 =1
//    0|1=1    0|0=0    与0相或不改变
void main(){
    unsigned char ch=169;    //1010 1001
    unsigned char ch1=15;    //0000 1111
                            //1010 1111        实现低四位全部变1
    printf("%d\n",ch|ch1); 
    system("pause");
}

四、异或运算　^（相同为0，相异为1）

不借助中间变量，实现两变量交换值

#include<stdio.h>
#include<stdlib.h>

//异或    1^1=0    1^0=1    0^1=1    0^0=0
void main0(){
    unsigned char ch1=169;    //1010 1001
    unsigned char ch2=15;    //0000 1111 
                            //1010 0110        166
    printf("%d\n",ch2^ch1); 
    system("pause");
}

//异或可以实现反转
void main1(){
    unsigned char ch1=169;    //1010 1001
    unsigned char ch2=255;    //1111 1111        全部反转
                            //0101 0110        86
    printf("%d\n",ch2^ch1); 
    system("pause");
}
void main2(){
    unsigned char ch1=169;    //1010 1001
    unsigned char ch2=60;    //0011 1100        指定位反转（中间反转）
                            //1001 0101        149
    printf("%d\n",ch2^ch1); 
    system("pause");
}


//异或交换两个变量
//不借助中间变量，实现两个变量的交换——>面试和嵌入式开发
//x，y交换值    x=x^y;y=x^y;x=x^y
/*
    等同于加减法实现交换值
    x=20,y=10;
    x=x+y;        //x=30,y=10
    y=x-y;        //x=30,y=20
    x=x-y;        //x=10,y=20
*/
void main(){
    unsigned char ch1=20;    //0001 0100
    unsigned char ch2=10;    //0000 1010        
    printf("%d，%d\n",ch1,ch2); 

    ch1=ch1^ch2;
    ch2=ch1^ch2;
    ch1=ch1^ch2;
    
    printf("交换之后%d，%d\n",ch1,ch2); 
    system("pause");
}

五、位运算总结

#include<stdio.h>
#include<stdlib.h>

void main(){
    unsigned char ch1=168;                //1010 1000
    unsigned char ch2=133;                //1000 0101    

    printf("&与：%d\n",ch1&ch2);        //1000 0000        128
    printf("|或：%d\n",ch1|ch2);        //1010 1101        173
    printf("^异或：%d\n",ch1^ch2);        //0010 1101        45
    unsigned char ch3=~ch1,ch4=~ch2;
    printf("~反：%d,%d        %d,%d\n",ch3,ch4,~ch1,~ch2);    
    system("pause");
}