Table of contents
Variable assignment and initialization
variable declaration
One of the features of PHP is that it does not require variables to be declared before they are used . A variable is created when it is assigned a value for the first time . Variables are used to store values such as numbers, text strings, or arrays. Once a variable is set, it can be reused in scripts.
Variables in PHP must be represented by a dollar sign $ followed by the variable name , using the assignment operation = to assign a value to a variable.
<?PHP
echo $name; //变量未定义，内存中没有创建该变量
$name = "HYC"; //变量的初始化赋值，会在内存中创建该变量
echo $name; //HYC
?>variable release
The unset() function releases the specified variable
unset($name); //release $name
variable naming
1. Variable names are strictly case-sensitive, and variables with different case are completely different.
2. The variable name is composed of letters, numbers, and underscores, and cannot start with a number, nor can it contain other characters (blank characters...)
3. Adopt camel case naming method
4. It is not recommended to use keywords as variable names
Variable assignment and initialization
When a variable is used for the first time, it is assigned a value. This process is called "initialization". When the variable is used later, the value of the variable can be modified at any time.
Directly use a = to complete the assignment of variables.
That is, it can be used directly by assigning a value to the variable.
mutable variable
A variable name can be dynamically set and used.
$$ is a feature of PHP, and it is also the cause of variable coverage vulnerabilities in PHP.
<?php
$name = "HYC";
$$name = "hello word"; //$ABC
echo $name;
echo "<hr />";
echo $ABC;
?>The final output is: HYC hello word
variable reference assignment
Simply understood as an alias for the variable
$b=$a;