php basic syntax
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?>
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>
<br>
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
PHP Variables
Variables are containers for storing information:
Example
<?php $x=5; $y=6; $z=$x+$y; echo $z; ?>
Running Example
Similar to Algebra
x=5 y=6 z=x+y
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"; ?>
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?>
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.";
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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