PHP Learning Notes (ii): Variable details, study notes _php tutorial

PHP Learning Notes (ii): Variable details, study notes

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 a number
2). Cannot use PHP operator (+-x/%&)
3). You can use the PHP keyword
4). Case-sensitive (PHP only variables, constants are case-sensitive)
5). Hump Naming method: 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 a value of $ A memory address to $b
$a = 2;
echo $b//Last value equals 1

Second, the variable data type

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 type
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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

Three, commonly used functions

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Isset ()///variable exists and a value of NULL means that it does not exist
Unset ()//release variable
Var_dump ()//Check the type of variable or value
Empty ()//The variable does not exist or returns True when NULL
Settype ($a, int)//Set Variable type
GetType ()//Get variable type

Four, variable declaration method

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$int = 10//integer 4-byte, Max 2³²
$float = 3.14e⁴//floating-point equals 3.14x10⁴
$bool = False//true is true
$str = "string"//double quotation mark can parse variable and escape character

You cannot use escape characters, but you can escape the single quotation mark itself for example $str = ' a\ ' a\ '
$str = ' string '

Declaring a string with a delimiter

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