课程章节：

课程名称：物联网/嵌入式工程师
章节名称：第1周之第三讲 3-6 C语言中的运算符：位运算符、赋值复合运算符、逗号运算符和三目运算符、运算符优先级
讲师姓名：大白老师

课程内容：

位运算符

代码示例 位运算

#include <stdio.h>

int main()
{
    unsigned char reg1 = 0x13;
    unsigned char reg2 = 0x78;
    unsigned char data = 0;

    data = reg1 & reg2;
    printf("data = %#x => %d\n",data,data);

    data = reg1 | reg2;
    printf("data = %#x => %d\n",data,data);
    
    data = reg1 ^ reg2;
    printf("data = %#x => %d\n",data,data);
    
    data = ~reg1;
    printf("data = %#x => %d\n",data,data);

    return 0;
}

分析：

0x13 => 0001 0011
0x78 => 0111 1000

&       0001 0000 => 0x10 => 16
|       0111 1011 => 4+2+1=7 8+0+2+1=11 => 0x7b => 123
^       0110 1011 => 4+2=6 8+0+2+1=11 => 0x6b => 107

0x13 => 0001 0011
~       1110 1100 => 14 12 => 0xec => 236

代码示例 位运算用处

#include <stdio.h>

int main()
{
    unsigned char a = 10; // 0000 1010
    unsigned char b = 15; // 0000 1111 8+4+2+1
    unsigned char t = 0;

    // a ^ a 
    //  0000 1010
    //^ 0000 1010
    //  0000 0000 

    // a ^ 0
    // 0000 1010
    //^0000 0000
    // 0000 1010

    printf("a = %d b = %d\n",a,b);

    a = a ^ b;
    b = a ^ b; // b = (a^b) ^ b => b = a ^ 0 => b=a
    a = a ^ b; // a = (a^b) ^ a => a = 0 ^ b => a=b

    printf("a = %d b = %d\n",a,b);
    return 0;
}

代码示例 移位运算

#include <stdio.h>

int main()
{
    unsigned char reg = 3;
    char a = -3;

    reg = reg << 3;
    printf("reg = %d\n",reg);

    a = a << 3;
    printf("a = %d\n",a);

    a = a>>3;
    printf("a = %d\n",a);
    return 0;
}

分析:

3 => 2+1 => 0000 0011
-3 => 
源码：1000 0011
反码：1111 1100
补码：1111 1101

3    0000 0011
<<3  0001 1000 => 16 + 8 = 24

-3   1111 1101
<<3  
补码：1110 1000
反码：1001 0111
+1 ：1001 1000 => -24

补码：1110 1000
>>3
补码：1111 1101
反码：1000 0010
+1 ：1000 0011 => -3

课后练习

unsigned char a = 0x58;  
unsigned char b = 0xd7;  
unsigned char c = 0;

 要求输出下列c的值。
 c = a & b,     
 c = a | b.   
 c = (a & ~b) ^ 0xf1;  
要求先笔算，然后书写代码验证。

代码：

#include <stdio.h>

int main()
{
    unsigned char a = 0x58;  
    unsigned char b = 0xd7;  
    unsigned char c = 0;

    c = a & b;
    printf("c = %#x => %d\n",c,c);// 0x50 80

    c = a | b;
    printf("c = %#x => %d\n",c,c);// 0xdf 223

    c = (a & ~b) ^ 0xf1; 
    printf("c = %#x => %d\n",c,c);// 0xf9 249
    
    return 0;
}

分析：

a = 0x58    
=> 4+1=5 8 => 0101 1000
b = 0xd7
=> d7 = 13 7 => 8+4+1=13 4+2+1=7 => 1101 0111

a 0101 1000
b 1101 0111
& 0101 0000 => 0x50 => 2^6+2^4=64+16=80

| 1101 1111 => 0xdf => 2^7+2^6+2^4+2^3+2^2+2^1+2^0 = 128+64+16+8+4+2+1 = 223

a&~b 
=> ~b 0010 1000
=>    0101 1000
=> &  0000 1000

=> 0xf1 => f=15 1 => 8+4+2+1=15 1 => 1111 0001

0000 1000
1111 0001
^
1111 1001 => 0xf9 => 2^7+2^6+2^5+2^4+2^3+2^0 = 128+64+32+16+8+1 = 249

赋值复合运算符

代码示例

#include <stdio.h>

int main()
{
    int a = 20,b = 10;
    
    a += b; // a = a + b;  => a = 30;
    printf("a = %d\n",a); //30

    a *= b; //a = a * b; => 30 * 10 
    printf("a = %d\n",a); //300

    return 0;
}

课后练习

练习
从键盘输入两个整数，要求输出+=,-=,*=,/=的结果

代码：

#include <stdio.h>

int main()
{
    int a,b,ret;
    printf("请输入两个整数：\n");
    scanf("%d%d",&a,&b);

    printf("a = %d b = %d\n",a,b);

    ret = a+=b;
    printf("ret = a+=b => a = %d b = %d ret = %d\n",a,b,ret);

    ret = a-=b;
    printf("ret = a-=b => a = %d b = %d ret = %d\n",a,b,ret);

    ret = a*=b;
    printf("ret = a*=b => a = %d b = %d ret = %d\n",a,b,ret);

    ret = a/=b;
    printf("ret = a/=b => a = %d b = %d ret = %d\n",a,b,ret);

    return 0;
}

逗号运算符和三目运算符

代码示例

#include <stdio.h>

int main()
{
    int a = 10,b = 20;
    int c = 0;
    int ret = 0;

    ret = a > b ? a+b : a-b;
    printf("ret = %d\n",ret);

    ret = a < b ? (a^=b ,b^=a ,a^=b) : a * b;
    printf("ret = %d\n",ret);

    ret = a < b ? (c = a,a = b,b = c) : a * b;
    printf("ret = %d\n",ret);

    return 0;
}

学习笔记：

课后练习

定义三个整数a,b,c，用户从键盘输入赋值,从小到大，排列，然后输出 [不允许使用if语句]
最终输出,a保存最小值，b保存其次，c保存最大值
例如:
用户输入 a = 30,b = 20,c = 10.要求最终保存的结果为
 a = 10,b = 20,c = 30.

代码：

#include <stdio.h>

int main()
{
    int a,b,c;
    printf("请输入三个整数：\n");
    scanf("%d%d%d",&a,&b,&c);

    printf("输入：a = %d b = %d c = %d\n",a,b,c);

    a > b ? (a^=b,b^=a,a^=b) : a;
    a > c ? (a^=c,c^=a,a^=c) : a;
    b > c ? (b^=c,c^=b,b^=c) : b;

    printf("输出：a = %d b = %d c = %d\n",a,b,c);

    return 0;
}

运算符优先级

运算符优先级规律

速记口诀

初等单目一二级 -> 初等运算符和单目运算符分别是第1、2优先级
乘除求余加减移 -> 这句里面的运算符全归为算术运算符，移表示移位
关系等于不等于 -> 关系运算符(< <= > >=)
按位与来异或或 -> 位运算符优先级顺序:& -> ^->l
逻辑与或条件弱 -> 逻辑运算符优先级顺序:&&->||，后面跟着优先级比较低(弱)的条件运算符
赋值逗号一点破 -> 赋值，逗号最低

课程评价：

通过了运算符学习，熟练掌握C语言中的位运算等操作。