Variables come from mathematics and are abstract concepts in computer language that can store calculation results or represent values. Variables can be accessed by variable name. In imperative languages, variables are usually mutable. Next we will introduce to you how to assign values to variables in PHP.
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1. Pass value assignment, for example$a=1,$b=$a, etc.;
2. Reference assignment , for example, $a=&$b, that is, $a and $b points to the same storage variable value address in the memory;
3. Reference counting value transfer, Objects in php and js are the default value transfer methods. It is a reference counting value. The example is as follows:
<?php
class Dog{
public $name="小花"；
public $leg=4;
}
$a=new Dog;//此时，$a指向了内存中的一个地址（假设0XFFAD[1]）,该地址又指向最终对象的值
$b=$a;//此时，$b和$a都指向了内存中的另一个地址（0XFFAD[2]），该地址又指向最终对象的值
var_dump($b->leg);//结果是int 4
$b=999;
var_dump($b);//结果是int 999;
var_dump($a);//此时的结果不是int 999，而是object(Dog)[1]Extended information
Variables come from mathematics and can be stored in computer languages. The result of a calculation may represent an abstract concept of value. Variables can be accessed by variable name. In imperative languages, variables are usually mutable; in purely functional languages, such as Haskell, variables may be immutable. In some languages, variables may be explicitly referred to as abstractions with storage space that can represent mutable state (such as in Java and Visual Basic); but other languages may use other concepts (such as objects in C) to refer to such variables. Abstract, but not strictly define the precise denotation of "variable".
Variables are useful because they allow you to give a short, easy-to-remember name to each piece of data you plan to use in your program. Variables can save data entered by the user when the program is running (such as using the InputBox function to display a dialog box on the screen, and then saving the text entered by the user into the variable), the results of specific operations, and a piece of data to be displayed on the form, etc. . In short, variables are simple tools for tracking almost any type of information.
If there is no value assigned after the variable is declared, the compiler will automatically prompt and assign a default value.
A variable is a convenient placeholder used to reference a computer memory address, which can store program information that can be changed when the Script is running. For example, you can create a variable called Click Count to store the number of times a user clicks on an object on a web page. Using variables does not require knowing the address of the variable in computer memory. You can view or change the value of the variable by referencing the variable by its name.
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