PHP variables and operators

This article introduces the variables and operators of PHP, which has certain reference value. Now I share it with you. Friends in need can refer to itVariable variables
is to add $ in front of the variable name, and the value of the variable inside is used as the name of the variable
Quoting the variable
is equivalent to giving the variable a Other names
& are address symbols
Note
1. Only variables can be referenced
2. When one variable is referenced and one changes, the other also changes.
3. When a variable is unset by reference and passed by value, the reference relationship is only released. If the unset variable is referenced by another variable, the unset variable will not release the memory, but only destroy the name of the variable
Constant
Constant is a single value An identifier, a quantity that cannot be modified or destroyed again after the definition is completed
Function
It cannot be changed by program in the future, so it is safer than a variable
Declaration
define('constant name','constant value')
Note
before the constant name Do not add $
The names of constants are case-sensitive by default. We generally use uppercase to declare variables
If the constant does not exist, it will be treated as a string. Processing, but the efficiency is relatively slow
The constant cannot be released, and an error will be reported if unset
The value of the constant cannot be a resource
System constants
PHP_VERSION The version of the php program
Magic constants
will change with unknown changes in the code
__LINE__Current line number
__FILE__The full path of the current script
__DIR__The absolute path of the directory where the current script is located
Use defined ('constant name') to determine whether a constant exists
Operator
Operator division
Unary operation
Binary operation
Ternary operation
Division of functions
If If there is a string in the operand, you need to convert the string into an integer or floating point number first
1. Arithmetic operator
- * /
%Remainder (modulo)
1. The sign of the modulo depends entirely on the first number
2. If the first number is less than the The result of modulo two numbers is the first number
Self-adding and self-decreasing
Note: (--) can be placed in front of the operand It can also be placed after the operand, but the meaning is different.
is placed after the operand, used first and then added/subtracted.
is placed in front of the operand. Add/subtract first and then use
Note: Boolean types do not participate in self-increment/self-decrement
2. The assignment operator
will wait. The value on the right side of the number is given to the variable
=
$a =1 which is equivalent to $a=$a 1
-=
$a-=1 is equivalent to $a=$a-1
*=
$a-=1 is equivalent to In $a=$a*1
/=
$a-=1 it is equivalent to $a=$a/1
%=
$a-=1 is equivalent to $a=$a%1
.=
$a .='a' is equivalent to $a=$a.'a'
3. Comparison operator
The result value of the comparison operator is of Boolean type
> Greater than sign
< Less than sign
>= Greater than or equal to
<= Less than or equal to
== Equal sign
Note: one = means assignment, two == means equal. Three === means all equal (values ​​and types need to be the same)
php is a weakly typed language that allows values ​​of different types to be compared. (During the comparison process, two different types will be converted into the same type first)
!= is not equal to
!== is not exactly equal to
Unique spaceship in php7
$a<=>$b
The result is 0, which means $a is equal to $b
The result is 1, which means $a is greater than $b
The result is -1, which means $a is less than $b
small tool
isset( )
Check whether the variable exists and return true if the value exists and is not null. Otherwise return false
empty()
Check whether the variable is empty
If the variable is empty
0
##“ ”
“0”
null
false
array() empty arrayVariable variable

is to add $ in front of the variable name, and the value of the variable inside is used as the name of the variableQuote variable

is equivalent to giving the variable another name
& is the address symbol
Note
1. Only variables can be referenced
2. When one of the referenced variables changes, the other one also changes
3. When a variable is unset by reference and passed by value, it just The reference relationship is released. If the unset variable is referenced by another variable, then the unset variable will not release the memory, but only destroy the name of the variable Constant

Constant is the identifier of a single value, and the definition is complete A quantity that cannot be modified and destroyed again
Function
It cannot be changed later by a program, so it is safer than a variable
Declaration
define('constant name','constant value')
Note
Do not add $ in front of the constant name
The names of constants are case-sensitive by default. We generally use uppercase when declaring variables.
If the constant does not exist, it will be processed as a string, but this efficiency Relatively slow
Constant cannot be released, and an error will be reported if unset
The value of the constant cannot be a resource
System constant
PHP_VERSION The version of the php program
Magic constant
will change with unknown changes in the code
__LINE__Current line number
__FILE__Full path of the current script
__DIR__Absolute path of the directory where the current script is located
Use defined ('constant name') to determine whether a constant existsOperator

Operator division
Unary operation
Binary operation
Ternary operation
Division of functions
If there is a string in the operand, the string needs to be converted first For integers or floating point numbers
1, arithmetic operators
- * /
% take remainder (modulo)1. The sign of the modulus depends entirely on the first number
2. If the first number is less than the second number, the result of the modulus is the first number.
Self-adding--Self-decrementing
Note: (--) can be placed before or after the operand, but the meaning is Different
is placed after the operand, used first and then added/subtracted.
is placed in front of the operand, added/subtracted first and then used
Note: Boolean types do not participate in self-increment/self-decrement
2. Assignment operator
assigns the value on the right side of the equal sign to the variable
=
$a =1 is equivalent to $a=$a 1
-=
$a-= 1 is equivalent to $a=$a-1
*=
##$a-=1 is equivalent to $a=$a*1
/=
$a-=1 is equivalent to $a=$a/1
%=
$a-=1 is equivalent to $a=$a%1
.=
$a.='a' is equivalent to $a=$ a.'a'
3. Comparison operator
The result value of comparison operator is Boolean type
> Greater than sign
< Less than sign
>= Greater than or equal to
<= Less than or equal to
== equal sign
Note: One = means assignment, two == means equal, three === means all equal (the value and type must be the same)
php is a weakly typed language that allows values ​​of different types to be compared. (During the comparison process, two different types will be converted into the same type first)
!= is not equal to
!== is not exactly equal to
Unique spaceship in php7
$a<=>$b
The result is 0, which means $a is equal to $b
The result is 1, which means $a is greater than $b
The result is -1, which means $a is less than $bGadget

isset()
Check whether the variable exists and return true if the value exists and is not null. Otherwise return false
empty()
Check whether the variable is empty
If the variable is empty
0
##“ ”
“0”
null
false
array() empty arrayRelated recommendations:

Understand the variable scope of php

php operators and Process analysis

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