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Basic learning about php

Apr 13, 2018 am 10:04 AM
phpBasestudy

The content introduced in this article is about the basic learning of PHP. Now I would like to share it with you. Friends in need can refer to it

1. PHP script with # It starts with ## and ends with ?>

<?php
// 此处是 PHP 代码
?>


2.

PHP supports three types of comments:

<?php
// 这是单行注释

# 这也是单行注释

/*
这是多行注释块
它横跨了
多行
*/
?>

3. PHP is case sensitive

3.1 All user-defined Functions, classes and keywords (such as if, else, echo, etc.) are not case-sensitive

##3.2

All variables are case-sensitive


##4. PHP variables

PHP variable rules:

Variables start with the $ symbol, followed by the name of the variable
  • Variable names must begin with a letter or underscore
  • Variable names cannot begin with a number
  • Variables Names can only contain alphanumeric characters and underscores (A-z, 0-9, and _)
  • Variable names are case-sensitive ($y and $Y are two different variables)


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)


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。


PHP global 关键词

global 关键词用于访问函数内的全局变量。请在(函数内部)变量前面使用 global 关键词。

<?php
$x=5;
$y=10;

function myTest() {
  global $x,$y;
  $y=$x+$y;
}

myTest();
echo $y; // 输出 15
?>

PHP 同时在名为 $GLOBALS[index] 的数组中存储了所有的全局变量。下标存有变量名。这个数组在函数内也可以访问,并能够用于直接更新全局变量。

<?php
$x=5;
$y=10;

function myTest() {
  $GLOBALS[&#39;y&#39;]=$GLOBALS[&#39;x&#39;]+$GLOBALS[&#39;y&#39;];
} 

myTest();
echo $y; // 输出 15
?>


PHP static 关键词

当函数完成/执行后,会删除所有变量。如果不想删除某个局部变量,首次声明变量时使用 static 关键词:

<?php

function myTest() {
  static $x=0;
  echo $x;
  $x++;
}

myTest(); //0
myTest(); //1
myTest(); //2
 
?>

每当函数被调用时,这个变量所存储的信息都是函数最后一次被调用时所包含的信息。该变量仍然是函数的局部变量。


5、echo 和 print 语句

  • 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 比 print 稍快,因为它不返回任何值。

echo print is a language structure and can be used with or without parentheses: echo or echo() print or print().


6、var_dump() will return variables The data types and values ​​of



7. Constants

有效的常量名以字符或下划线开头(常量名称前面没有 $ 符号);与变量不同,常量贯穿整个脚本是自动全局的。

使用 define() 函数 - 它使用三个参数:

  1. 首个参数定义常量的名称

  2. 第二个参数定义常量的值

  3. 可选的第三个参数规定常量名是否对大小写不敏感。默认是 false。


8、foreach循环

foreach 循环只适用于数组,并用于遍历数组中的每个键/值对

<?php 
$colors = array("red","green","blue","yellow"); 

foreach ($colors as $value) {
  echo "$value <br>";
}
?>


9、php函数

用户定义的函数声明以关单 "function" 开头。

函数名能够以字母或下划线开头(而非数字)。

函数名对大小写不敏感。


10、php数组

 array() 函数用于创建数组

  • 索引数组 - 带有数字索引的数组

  • 关联数组 - 带有指定键的数组

  • 多维数组 - 包含一个或多个数组的数组


遍历关联数组

<?php
$age=array("Bill"=>"35","Steve"=>"37","Peter"=>"43");

foreach($age as $x=>$x_value) {
  echo "Key=" . $x . ", Value=" . $x_value;
  echo "<br>";
}
?>


11、数组排序


  • sort() - 以升序对数组排序

  • rsort() - 以降序对数组排序

  • asort() - 根据值,以升序对关联数组进行排序

  • ksort() - 根据键,以升序对关联数组进行排序

  • arsort() - 根据值,以降序对关联数组进行排序

  • krsort() - 根据键,以降序对关联数组进行排序


12、全局变量 - 超全局变量


$GLOBALS — References all variables available in the global scope

PHP stores this in an array named $GLOBALS[index] All global variables. The name of the variable is the key of the array.


$_SERVER This superglobal variable holds information about headers, paths, and script locations.


#$_REQUEST is used for collection HTML form submitted data.


#$_POST Widely used to collect form data after submitting an HTML form with method="post". $_POST is also commonly used to pass variables.


##$_GET

can also be used to collect and submit HTML forms (method=" form data after get").

$_GET can also collect data sent in the URL.

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