How to name variables in php?

Variables are containers for storing information. Just like algebra, PHP variables can be used to hold values ​​(x=5) and expressions (z=x y).

Variable names can be short (such as x and y) or more descriptive (such as carname, total_volume).

PHP variable naming rules

1. Variables start with the dollar sign $, followed by the name of the variable. Such as $name, $age.

2. The first character after the dollar sign $ cannot be a number, but can only be an underscore_ or a letter. Variables like $1_1 are wrong.

3. Variable names can only contain letters, numbers and underscores (A-z, 0-9 and _)

4. Except for the underscore _, variables do not allow any spaces or punctuation marks. That is to say, the variable name can only contain: a-z, A-Z, 0-9 and underscore_.

5. PHP variable names are case-sensitive. For example, $name and $Name are two different variables.

Remaining Notes on PHP Variable Naming Rules

1. When naming a variable with two or more words, you can use other than the first word Capitalize the first letter of all words. Such as $myName, $yourFamilyName.

2. Variables named starting with underscore _ usually represent special variables. Such as creating protected attributes, PHP predefined variables ($_GET), global arrays, etc. in the class.

3. When defining variables, do not be greedy for brevity. Instead, use descriptive names to define variables.

PHP variable scope

In PHP, variables can be declared anywhere in the script.

The scope of a variable refers to that part of the script where the variable can be referenced/used.

PHP has three different variable scopes:

● Local (local)

● Global (global)

● static (static)

Example:

<?php
$x=5; // global scope
  
function myTest() {
   $y=10; // local scope
   echo "<p>在函数内部测试变量：</p>";
   echo "变量 x 是：$x";
   echo "<br>";
   echo "变量 y 是：$y";
} 

myTest();

echo "<p>在函数之外测试变量：</p>";
echo "变量 x 是：$x";
echo "<br>";
echo "变量 y 是：$y";
?>

Output:

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