PHP Beginner Basics

Introduction to basic knowledge of PHP summary and introduction to the detailed explanation.

One, PHP script code tag

PHP script is a pair of special tags in the file included content, such as ASP is "<%....%>", PHP can be seen as "<?...? > ".

However, in order to adapt the XML standard to embed PHP in XML or XHTML, PHP does not recommend using short form "<?...? >, and recommended long format tags "<?php ...?" > "

In addition, the PHP code block also supports the <script language= "php" >...</script> tag form.

Two, PHP instruction separator

Each statement in PHP needs to be separated by a semicolon ";", but for the PHP closing tag "?>", it automatically implies a semicolon, so there is no need to append a semicolon.

So, the format of a PHP script can be as follows:

<?php
/*
............ ;
............ ;
............ ;
............
*/
Note that the last line can have no semicolon
?>

Three, PHP comments

PHP Multiline Annotations Use the "/* ... *"

Single-line comments Use "#" or "//"

Four, the output of PHP

In ASP, use the "<%=...%>" fast output line, or use "<%response.write" ("...")%> "

Use "echo ()" or "print ()" Directly in PHP, such as:

<?php
echo "a";
Echo (b);
Echo ("C");
Echo D;
?>

The output is "ABCD" and the above four types are normally output.

But this is in the ASP, especially echo "a"; and Echo D; is output to the string itself, and is not possible. This requires understanding the variable definition of PHP.

Five, PHP variables

Like the ASP, PHP variables can be used without first defining them directly. For the type of the variable, automatically generated when the value is assigned.

Various variables in PHP are preceded by a "$" in the variable name to differentiate.

<?php
$a = "123";
echo A;
echo $a;
?>

Enter as "A123"

Six, the single and double quotes in PHP

<?php
$a = "123";
echo "$a";
echo ' $a ';
?>

The output is "123$a", where echo "$a" outputs the value of variable A, and echo ' $a ' outputs the string itself in single quotes.

<?php
$a = "123";
echo "$a ' $a '";
?>

The output of "123 ' 123" is not "123$a". Although it is ' $a ', the variable is replaced with double quotes.

So it can be concluded that as long as the variables in the contents of the double quotes are substituted, the single quotes are not replaced.

The contents of the double quotes should be escaped using the "\" prefix, such as "\", "\$", "\". So to enter "123$a";

<?php
$a = "123";
echo "$a \ $a";
?>

Another example:

<?php
$a = "123";
echo "$a \ $a \ \";
?>

The output is "123$a" \ ".

ASP transfer PHP need to note:

1, delimiter comma ";" Easy to forget to write.
2, the definition and use of variables.
3, the use of single and double quotes.