Summary of commonly used special operation symbols and functions in PHP (a must-read for newbies to PHP)_PHP Tutorial

注解符号:
         // 单行注解   
             多行注解
引号的使用
         '   ' 单引号,简单字符串,不经任何处理直接拿过来;
         " "双引号,php动态处理然后输出,一般用于处理$变量.
布尔变量:  
          一种是true 即 真的;
         另一种是false 即假的
常见变量:  
         string          字串(数字\汉字\等等)
         integer         整数(1、2、3、4、5、0、-1、-2、等等)
         double          浮点数（小数点）
         array           数组 
         object          对象
可以用的方法有gettype($mix) 和settype($mix,$typename);

常用符号转义：

" " Double quotes
" \ Backslash
n n Line feed
r Return to the beginning of the line
t Horizontal tabulation
Arithmetic symbols:
+ Addition operation -Rugging operations *multiplication operation /division of the method
%remains ++ self -plus 1
-self -reduction 1. Connect two string

assignment operation:

/= Divide the value on the left by the value on the right
.= Add the string on the right to the left

Bitwise operations:

^ Bitwise exclusive OR (xor)                                                                                        != is not equal to && and || or ! Other operation symbols other than



$ Variable symbol
Alias ​​for variable
@ Do not display error message (added before function)
-> Object method or attribute
=> The element value of the array
?: Ternary operator

Commonly used basic methods:

1. PHP converts strings to upper and lower case!

strtolower(); Convert characters to lowercase
strtoupper(); Convert characters to uppercase

2.PHP encrypted string

Irreducible:
md5();
sha1();
Reducible:
base64_encode();
base64_decode();

3. About quotation marks

1. Single quotes are output as is
2. Double quotes are content interpretation and output
3. Anti-single quotes (small quotes) are used to execute a system command, such as `dir`. Commonly used in table names and field names.
4. "" acts on translation characters, such as "n" for newline.

4. Functions: htmlspecialchars() and htmlentities()
This function converts special characters into HTML string format ( &....; ). The most commonly used occasion may be the message board for processing customer messages.

& (and) is converted to &
" (double quotes) is converted to "
> (greater than) is converted to >
(space ) into

5. Batch output HTML content!

echo HTML output content. . . //Comments here are still output!
EOT;

print HTML output content. . . //Comments here are still output!
EOT;
(Note: Use "{variable}" for internally included variables)

6. Determine whether the file exists and output the content file_exists ()

$FileName="File.TXT";
if (file_exists($FileName)){
echo "

".file_get_contents($FileName)."&lt ;/pre>";<br>}else<br>{<br>echo "no";<br>}<br>?>
<p>7. Delete variables to release memory unset();</p>
<p>unset($var);<br>unset($var,$var1);</p>
<p>8.is_numeric;<br>Detect whether the variable is a number; </p>
<p>9.is_int;<br>Detect whether the variable is an integer;</p>
<p>10.is_null;<br>Detect whether the variable is NULL;</p>
<p>11.is_string<br>Detect whether the variable is a string</p>
<p>12.is_real;<br>alias of is_float()</p>
<p>13.isset<br>Check whether the variable is defined</p>
<p>14.is_bool<br>Detect whether the variable is of Boolean type</p>
<p>15.is_array<br>Detect whether the variable is an array</p>
<p>16.is_object<br>Detect whether the variable is an object</p>
<p>17.substr() function returns a part of the string. </p>
<p>substr (String,Start,SelectNum)<br></p><div class="codetitle">
<span style="CURSOR: pointer" onclick="doCopy('code86858')"><u>Copy code</u></span> The code is as follows:</div><div class="codebody" id="code86858">
<br>echo substr('abcdef', 1); // bcdef<br>echo substr('abcdef', 1, 3); // bcd<br>echo substr('abcdef', 0, 4); // abcd<br>echo substr('abcdef ', 0, 8); // abcdef<br>echo substr('abcdef', -1, 1); // f<br>
</div>
<p>18.nb2br() Convert the escaped newline into html<br><br></p><div class="codetitle">
<span style="CURSOR: pointer" onclick="doCopy('code78572')"><u>Copy code</u></span> The code is as follows:</div><div class="codebody" id="code78572">
<br>echo nl2br("foo isn'tn bar");<br>
</div>

<p align="left"></p><div style="display:none;">
<span id="url" itemprop="url">http://www.bkjia.com/PHPjc/326498.html</span><span id="indexUrl" itemprop="indexUrl">www.bkjia.com</span><span id="isOriginal" itemprop="isOriginal">true</span><span id="isBasedOnUrl" itemprop="isBasedOnUrl">http: //www.bkjia.com/PHPjc/326498.html</span><span id="genre" itemprop="genre">TechArticle</span><span id="description" itemprop="description">Annotation symbols: // Use of single-line annotation and multi-line annotation quotation marks ' ' Single quotation mark, simple string, without Take any processing directly; " "Double quotes, php dynamic processing and then output, generally used for processing...</span>
</div>
<div class="art_confoot"></div>