PHP Learning Notes (ii): _php Examples of variable detailed

Introduction of PHP Variables

1. Grammar

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PHP is a weakly typed language, and the variable type is determined by the stored value
Strongly typed language: int a = 1
$ Variable name = value

2. Naming rules

1). Cannot start with numbers
2). Cannot use PHP operator (+-x/%&)
3). You can use the PHP keyword
4). Case Sensitive (PHP is only variable, constant case sensitive)
5). Hump nomenclature: AABBCC (first letter lowercase)

3. Variable variable

Variable names can be set dynamically, for example: $ $var

4. Reference Assignment

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$a = 1;
$b =& $a; Assigns the value of the $a memory address to $b
$a = 2;
echo $b//Last value equals 1

Second, variable data types

1, four kinds of scalar

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int (integer), bool (Boolean), float,double (floating-point penalty), string (string)

2, two kinds of compound

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Arrays: Array ()
Objects: Object
For example: $var = new Mysqlli (' localhost ', ' root ', ' 123455 ')

3, two kinds of special types

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Resource (resources) For example: $var = fopen (' test.php ', ' R ')
Null (NULL type) is case-insensitive

Iii. Common functions

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Isset ()///variable exists, value NULL indicates no
Unset ()//release variables
Var_dump ()//Check the type of variable or value
Returns True if Empty ()///variable does not exist or is empty
Settype ($a, int)//Set Variable type
GetType ()//Get variable type

Four, variable declaration method

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$int = 10//int 4 bytes, maximum 2³²
$float = 3.14e⁴//floating-point type equals 3.14x10⁴
$bool = False//true is true
$str = "string"//double quotes to resolve variables and escape characters

You cannot use escape characters, but you can escape the single quotes themselves such as $str = ' a\ ' a\ '
$str = ' string '

declaring strings with delimiters