[arithmetic, relation, logic, bit, compound assignment, self increasing, self decreasing and other] operators (learning note 4 -- C language operators)

Preface ：
If you are learning C Language without knowing where to start , You can study with me C Language , During the winter vacation, I will post a blog every day , There are all kinds of C The knowledge of language , If you want to learn , Want to improve , Come and punch in with me every day , I hope we can make progress together .

C Language operators can be seen from the number of logical numbers , Can be divided into one item 、 Two eyes 、 Ternary operator .

One 、 Arithmetic operator

Operator	effect	Example	result
+	Add the left and right operands	7+4	11
-	Subtract the left and right operands	7-4	3
*	Multiply the left and right operands	7*4	28
/	Divide the left and right operands	7/4	1
%	Modulo the left and right operands ( Seeking remainder ) operation	7%4	3

These five arithmetic operators are binary operators , The function of arithmetic operators is to evaluate .
Multiplication 、 division 、 Modulo operators take precedence over addition 、 Subtraction has high priority .

1. Implicit conversion

When performing arithmetic operations , In the left and right operands , The operation will be based on the largest data type , That is, the smaller data type will be converted to the larger data type first , And then we do the calculation . The process of automatically converting small types to large types , We call it “ Implicit type conversion ”.
Here are some common :

char < int < float < double
7 / 4 = 1
7.0 / 4 = 1.75
7 / 4.0 = 1.75

2. In division operations , The divisor cannot be zero 0

If the divisor is 0, You get the wrong results .

3. In modulo operation, both operands should be integers

And only the left operand will affect the positive and negative relationship of the result , That is, if the left operand is positive , Then the module result is also positive . conversely , If the left operand is negative, the modulo result is also negative .

7 % -4 = 3
-7 % 4 = -3

Two 、 Relational operator

Operator	effect	Example	result
==	Compare the left and right operands for equality	5 == 8	0
!=	Compare whether the left and right operands are not equal	5 != 8	1
<	Compare whether the left operand is less than the right operand	5 < 8	1
<=	Compare whether the left operand is less than or equal to the right operand	5 <= 8	1
>	Compare whether the left operand is greater than the right operand	5 > 8	0
>=	Compare whether the left operand is greater than or equal to the right operand	5 >= 8	0

The above relational operators are binary operators , To compare the size relationship between the left and right operands .
C Language use 1 To show the truth , use 0 To show false . But the true value is not just 1, But any non-zero value . It's just that they usually use 1 To show the truth .

3、 ... and 、 Logical operators

Operator	type	effect	Example	result
!	Monocular	Get a logical value of the inverted operand	! 0(! 1)	1（0）
&&	Binocular	When both the left and right logical values are true , The result is true , All other cases are false	1&&1 (0&&1、1&&0、0&&0)	1（0）
||	Binocular	When both the left and right logical values are false , The result is false , The results of other cases are all true	0||1、1||0、1||1 (0||0)	1（0）

1. Short circuit effect

When using logical and operators , If the result of the left operand is false , The direct return result is false , Instead of checking the right operand .
When using logical or operators , If the result of the left operand is true , The direct return result is true , Nor will we check the right operand .

Four 、 An operator

Operator	name	effect	type
<<	Bitwise shift left operator	Turn all positions to the left （ High position ） Move , Low complement 0	Binocular
>>	Bitwise shift right operator	Turn all positions to the right （ Low position ） Move , The high bit is mandatory for unsigned types 0, For signed types, the sign bit is continued	Binocular
~	Bitwise negation operator	Invert all bits （1 Turn into 0,0 Turn into 1）	Monocular
&	Bitwise and operator	And operate the two operands bit by bit	Binocular
|	bitwise or operator	To perform a bitwise OR operation on two operands	Binocular
^	bitwise exclusive or operator	Bitwise exclusive or of two operands	Binocular

Logical operators operate on operands , Bit operators operate on the binary bits of operands .
The following pairs of integers 23, Its 8 Bit binary code is 0001 0111

23<<1
have to 0010 1110

23>>1
have to 0000 1011

~23
have to 1110 1000

23&50
have to 0001 0010

23|50
have to 0011 0111

23^50
have to 0010 0101
（ Exclusive or ： Two different , One for 1, One for 0, The result is 1）

5、 ... and 、 Compound assignment operator

Operator	effect	Example	amount to
+=	Add the left variable value to the right operand and assign it to the left variable	a += 1	a = a + 1
-=	The left variable value is subtracted from the right operand and then assigned to the left variable	a -= 1	a = a - 1
*=	The left variable value is multiplied by the right operand and then assigned to the left variable	a *= 1	a = a * 1
/=	Divide the value of the left variable by the right operand and assign it to the left variable	a /= 1	a = a / 1
%=	The left variable value and the right operand are modulo assigned to the left variable	a %= 1	a = a % 1
<<=	Move the left variable value to the left bit by bit, and assign the value to the left variable after positioning the right operand	a <<= 1	a = a << 1
>>=	Shift the value of the left variable to the right bit by bit, and assign the value to the left variable after positioning the right operand	a >>= 1	a = a >> 1
&=	The left variable value and the right operand are bitwise summed, and then assigned to the left variable	a &= 1	a = a & 1
|=	Assign the left variable value to the left variable after bitwise or with the right operand	a |= 1	a = a | 1
^=	Assign the left variable value to the left variable after bitwise exclusive or with the right operand	a ^= 1	a = a ^ 1

These operators can only be used with modifiable variables , Not available for constants .

6、 ... and 、 Operators with side effects

Assignment operator 、 Compound assignment operator 、 Self increasing 、 Self - subtracting operator .
We usually call these behaviors that can change operands “ side effect ”, Operators with such behavior are called “ Operators with side effects ”.

7、 ... and 、 Self increasing 、 Self - subtracting operator

It's a unary operator , It is also an operator with side effects .
a The initial value for the 1

Operator	form	effect	Example	result
++	Prefix self incrementing	Add the operands to 1 And returns the new value of the operand	++a	2
++	Suffixes increase	Add the operands to 1 And returns the original value of the operand	a++	1
- -	The prefix subtracts itself	Subtract... From the operands 1 And returns the new value of the operand	- -a	0
- -	Suffix subtraction	Subtract... From the operands 1 And returns the original value of the operand	a- -	1

If we simply want the operands to add 1, Instead of using this new value , No matter the prefix or suffix autoincrement operators are used ; On the contrary, if you need to use this new value , There is a difference between prefix and suffix .

8、 ... and 、 Other operators

1. Type conversion operators （）

The behavior of automatically converting small types to large types is implicit type conversion .
Now let's talk about the display type conversion , It can not only convert a small type to a large type like implicit type conversion , You can also convert a large type to a small type , This cannot be done by implicit type conversion .

( data type ) Operands
The data type in parentheses indicates the destination data type to be converted .

2. The comma operator

int a;
a =(3,4,5);
The result is 5

int a;
a = 3,4,5;
The result is 3

3. Conditional operator

It's a trinary operator

Operands 1 ？ Operands 2 ： Operands 3
If the operands 1 It's true , Returns the operand 2, Otherwise, return the operand 3.

4.sizeof Operator

sizeof ( Operands );
This operand can be a data type , It can also be a constant or variable of some data type .
If operand is a data type , Then you must use parentheses , If the operand is not a data type , You can omit the parentheses .

sizeof Operator to return its size , In bytes . adopt sizeof Operator can easily know the amount of space occupied by a data type in memory .