C language - shift operator

Table of contents

left shift operator

right shift operator 

arithmetic right shift

 logical shift right

Summarize

---

What is stored in memory is two's complement.

So the shift operator is to shift the two's complement .

Take the left shift operator as an example: <<

---

left shift operator

For positive numbers:

#include<stdio.h>
int main()
{int a=10;
//00000000000000000000000000001010——补码  //正数原码反码补码相同
int b=a<<1;  //左移1
printf("%d\n",b);
printf("%d\n",a);
return 0;
}

Process: Result:

Note: a does not change during this process.

For negative numbers:

#include<stdio.h>
int main()
{int a=-10;
//10000000000000000000000000001010——原码
//11111111111111111111111111110101——反码   //取反
//11111111111111111111111111110110——补码   //加一
int b=a<<1;  //左移1
//11111111111111111111111111101100——补码
//11111111111111111111111111101011——反码   //减一
//10000000000000000000000000010100——原码   //取反
printf("%d\n",b);
printf("%d\n",a);
return 0;
}

Process: Result:

 Note: What we print is the original code.

            a remains unchanged.

Findings: 1. The rule is: discard on the left and fill in zeros on the right.

           2. Shifting one bit to the left has the effect of multiplying by 2.

---

right shift operator 

Right shift operators are divided into arithmetic right shift and logical right shift .

It depends on the compiler, arithmetic right shift is more common .

 

arithmetic right shift

#include<stdio.h>
int main()
{
	int a = -1;
	//10000000000000000000000000000001——原码
	//11111111111111111111111111111110——反码
	//11111111111111111111111111111111——补码
	
    int b = a>>1;
    //11111111111111111111111111111111——补码
    //11111111111111111111111111111110——反码
    //10000000000000000000000000000001——补码
	
    printf("%d\n", b);
	printf("%d\n", a);
	return 0;
}

 Process: Result:

 

 logical shift right

#include<stdio.h>
int main()
{
	int a = -1;
	//10000000000000000000000000000001——原码
	//11111111111111111111111111111110——反码
	//11111111111111111111111111111111——补码
	
    int b = a>>1;
    //01111111111111111111111111111111——补码
    //01111111111111111111111111111110——反码
    //00000000000000000000000000000001——补码
	
    printf("%d\n", b);
	printf("%d\n", a);
	return 0;
}

process:

 Discovery: 1. Arithmetic right shift: the right side is discarded, and the left side complements the original sign bit.

            2. Logical right shift: discard on the right and fill with zeros on the left.

---

Summarize

Left shift operator: discard on the left and pad with zeros on the right.

Arithmetic right shift: the right side is discarded, and the left side is filled with the original sign bit.

Logical shift right: discard on the right and pad with zeros on the left.

Note: There is no right/left shift of negative numbers.