Table of Contents
Basic PHP syntax
PHP case sensitivity
Example
PHP Variables
Similar to Algebra
PHP 变量规则:
PHP 是一门类型松散的语言
PHP 变量作用域
Local 和 Global 作用域
实例
PHP global 关键词
PHP echo 和 print 语句

php basic syntax

Jun 11, 2018 pm 11:35 PM
php

Basic PHP syntax

PHP scripts can be placed anywhere in the document.

PHP scripts start with and end with ?>:

<?php// 此处是 PHP 代码?>
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The default file extension for PHP files is ". php".

PHP files usually contain HTML tags and some PHP script code.

PHP case sensitivity

In PHP, all user-defined functions, classes and keywords (such as if, else, echo, etc.) are not case-sensitive.

In the following example, all three echo statements are legal (equivalent):

Example

<!DOCTYPE html>
<html>
<body>
<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>
</body>
</html>
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<br>
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However, in PHP, all variables are valid Case Sensitive.

In the following example, only the first statement will display the value of the $color variable (this is because $color, $COLOR, and $coLOR are considered three different variables):

Example






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PHP Variables

Variables are containers for storing information:

Example

<?php
$x=5;
$y=6;
$z=$x+$y;
echo $z;
?>
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Running Example

Similar to Algebra

x=5
y=6
z=x+y
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In algebra we use letters (like x) to hold values ​​(like 5).

From the above expression z=x y, we can calculate that the value of z is 11.

In PHP, these three letters are called variables.

注释:请把变量视为存储数据的容器。

PHP 变量规则:

  • 变量以 $ 符号开头,其后是变量的名称

  • 变量名称必须以字母或下划线开头

  • 变量名称不能以数字开头

  • 变量名称只能包含字母数字字符和下划线(A-z、0-9 以及 _)

  • 变量名称对大小写敏感($y 与 $Y 是两个不同的变量)

PHP 是一门类型松散的语言

在上面的例子中,请注意我们不必告知 PHP 变量的数据类型。

PHP 根据它的值,自动把变量转换为正确的数据类型。

在诸如 C 和 C++ 以及 Java 之类的语言中,程序员必须在使用变量之前声明它的名称和类型。

PHP 变量作用域

在 PHP 中,可以在脚本的任意位置对变量进行声明。

变量的作用域指的是变量能够被引用/使用的那部分脚本。

PHP 有三种不同的变量作用域:

  • local(局部)

  • global(全局)

  • static(静态)

Local 和 Global 作用域

函数之外声明的变量拥有 Global 作用域,只能在函数以外进行访问。

函数内部声明的变量拥有 LOCAL 作用域,只能在函数内部进行访问。

下面的例子测试了带有局部和全局作用域的变量:

实例

测试函数内部的变量:

";   echo "变量 x 是:$x";   echo "<br>";   echo "变量 y 是:$x"; }  myTest(); echo "

测试函数之外的变量:

"; echo "变量 x 是:$x"; echo "<br>"; echo "变量 y 是:$x"; ?>
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PHP global 关键词

global 关键词用于访问函数内的全局变量。

要做到这一点,请在(函数内部)变量前面使用 global 关键词:

实例

<?php
$x=5;
$y=10;
function myTest() {
  global $x,$y;
  $y=$x+$y;
}
myTest();
echo $y; // 输出 15?>
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PHP echo 和 print 语句

echo 和 print 之间的差异:

  • echo - 能够输出一个以上的字符串

  • print - 只能输出一个字符串,并始终返回 1

echo "I'm about to learn PHP!<br>";
echo "This", " string", " was", " made", " with multiple parameters.";
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本文讲解了php基本语法,更多相关内容请关注php中文网。

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