Chapter 2 PHP basics-php code writing

1. Several PHP code embedding styles on web pages
Standard or short style is recommended
Copy codeThe Code is as follows:
<? Php
// Standard style
Echo 'Hello World! ';
?>
<?
// Short style
Echo 'Hello World! ';
?>
<Script language = "php">
// Script style
Echo 'Hello World! ';
</Script>

2. Four Methods of code annotation
Copy codeThe Code is as follows:
<? Php
// Single line comment
/*
* Multi-line comment
*/
# Shell style comment
/**
* PHPdoc style Annotation
*/
?>

3. Several Methods for outputting strings to the browser
Copy codeThe Code is as follows:
<? Php
/*
* Echo function: outputs a string to the browser.
* Function return value: void
*/
Echo 'echo function! ';
Echo ('<br/> ');
/*
* Echo function: outputs a string to the browser.
* Function return value: int
*/
Print 'print function ';
Echo ('<br/> ');
Echo print 'echo value of print function .';
Echo ('<br/> ');
/*
* Printf function: outputs a string to the browser.
* Function return value: the length of the printed string
*/
Printf ("a weekend have % d days", 7 );
Echo ('<br/> ');
Echo printf ("a weekend have % d days", 7 );
Echo ('<br/> ');
/*
* Sprintf function: saves the string to the memory.
* Function return value: the saved string itself.
*/
Sprintf ('sprintf function ');
Echo ('<br/> ');
Echo sprintf ('sprintf function ');
Echo ('<br/> ');
?>

Output result:
Echo function test!
Print function test.
Print function test. 1
A weekend have 7 days
A weekend have 7 days. 23
Sprintf function test
Common Type Indicator

Type	Description
% B	Integer in binary format
% C	Integer, displayedASCIICharacter
% D	Integer, displayed as a signed decimal number
% F	Floating Point Number, displayed as a floating point number
% O	Integer, which is displayed as the octal number
% S	String, displayed as a string
% U	Integer. It is displayed as an unsigned decimal number.
% X	An integer in hexadecimal format.
% X	An integer in upper-case hexadecimal format.

Iv. Identifiers and variables
1. Basic rules for identifiers:
1) An identifier can be of any length and can contain any letter, number, or underline.
2) The identifier cannot start with a number.
3) in PHP, identifiers are case sensitive.
4) A variable name can be the same as a function name.
2. Variable assignment:
Copy codeThe Code is as follows:
<? Php
$ Sum = 0;
$ Total = 1.22;
$ Sum = $ total;
Echo $ sum; // 1.22
?>

3. Data Type of the variable:
Basic Data Type

Type	Name
Integer	Integer
Float	Single-precision floating point number
Double	Precise floating point number
String	String
Boolean	Boolean
Array	Array
Object	Object

4. Type strength
PHP is a dynamic language and a very weak type language. When running a program, you can dynamically change the type of the variable.
5. type conversion:
Implicit type conversion:
Copy codeThe Code is as follows:
<? Php
$ Sum = 0;
$ Total = 1.22;
$ Sum = $ total;
Echo gettype ($ sum); // double
?>

Explicit type conversion:
Copy codeThe Code is as follows:
<? Php
$ Sum = 100;
$ Total = (string) $ sum;
Echo gettype ($ sum); // string
?>

Use the settype () function for type conversion. The return value 1 indicates that the conversion is successful, and the null value indicates that the conversion is failed.
Copy codeThe Code is as follows:
<? Php
$ Sum = 58;
Echo settype ($ sum, "float ");
Echo $ sum; // 58
Echo gettype ($ sum); // double
?>

6. Function for variable Detection:

Function	Function	Return Value
Gettype ()	Get the variable type	One of the basic data types
Settype ()	Set the variable type	Bool (1: true 0: false (or ''))
Isset ()	Used to determine whether a variable exists	Bool
Unset ()	Release a given variable	Void
Empty ()	Checks whether the value of a variable is null.	Bool
Is_int () is_integer ()	Check whether the variable is an integer.	Bool
Is_string ()	Checks whether the variable is a string.	Bool
Is_numeric	Checks whether the variable is a numeric or numeric string.	Bool
Is_null	Check whether the variable isNULL	Bool
Intval ()	Returns the integer of a variable.	Int

Basic use of Isset ()
Copy codeThe Code is as follows:
<? Php
$ A = 10;
Echo isset ($ a); // 1
?>
<? Php
Echo isset ($ B );//''
?>

Basic usage of Usset ()
Copy codeThe Code is as follows:
<? Php
$ A = 10;
Unset ($ );
Echo isset ($ );//''
?>

Basic use of Empty ()
Copy codeThe Code is as follows:
<? Php
$ A = 5;
$ B = 1;
$ C = 0;
$ D = "";
$ E = array ();
$ F = null;
$ G = "0 ";
$ H = false;
Echo empty ($ a); // ''(false)
Echo '<br/> ';
Echo empty ($ B); // ''(false)
Echo '<br/> ';
Echo empty ($ c); // 1 (true)
Echo '<br/> ';
Echo empty ($ d); // 1 (true)
Echo '<br/> ';
Echo empty ($ e); // 1 (true)
Echo '<br/> ';
Echo empty ($ f); // 1 (true)
Echo '<br/> ';
Echo empty ($ g); // 1 (true)
Echo '<br/> ';
Echo empty ($ h); // 1 (true)
Echo '<br/> ';
Echo empty ($ f); // 1 (true)
?>

Is_int. Similar functions include: is_float (), is_double (), is_string (), is_bool (), is_array (), is_null (), is_long (), is_object (), is_resource () is_numeric (), is_real (), etc.
Copy codeThe Code is as follows:
<? Php
$ A = 11;
$ B = 1.23;
$ C = 3.1415926;
$ D = "hello ";
$ E = false;
$ F = array ();
$ G = null;
Echo is_int ($ a); // 1
Echo '<br/> ';
Echo is_float ($ B); // 1
Echo '<br/> ';
Echo is_double ($ c); // 1
Echo '<br/> ';
Echo is_string ($ d); // 1
Echo '<br/> ';
Echo is_bool ($ e); // 1
Echo '<br/> ';
Echo is_array ($ f); // 1
Echo '<br/> ';
Echo is_null ($ g); // 1
Echo '<br/> ';
Echo is_numeric ($ a); // 1
?>

Basic use of Intval () functions. Similar functions: floatval (), strval ()
Copy codeThe Code is as follows:
<? Php
$ A = 22.23;
Echo gettype ($ a); // double
Echo '<br/> ';
$ B = intval ($ a); // the original type of $ a is not changed after type conversion.
Echo gettype ($ a); // double
Echo '<br/> ';
?>
<? Php
$ A = 22.23;
Echo gettype ($ a); // double
Echo '<br/> ';
Settype ($ a, "integer"); // the original type of $ aa is changed after type conversion.
Echo gettype ($ a); // integer
Echo '<br/> ';
?>

7. Scope of Variables

Super global variable

Variable name	Function
$ GLOBALS	All global variable Arrays
$ _ SERVER	Server environment variable array
$ _ GET	Variable array passed to the script through GET
$ _ POST	Array of variables passed to the script in POST Mode
$ _ COOKIE	COOKIE variable array
$ _ FILES	Variable array related to File Upload
$ _ ENV	Environment variable array
$ _ REQUEST	Array of variables input by the user
$ _ SESSION	Session variable array

8. Constants
Once defined, it cannot be changed again.
Copy codeThe Code is as follows:
<? Php
Define ("TOTAL", 100 );
Echo TOTAL; // 100
Echo '<br/> ';
Define ("TOTAL", 200 );
Echo TOTAL; // 100
?>

Methods for viewing predefined PHP Constants
Copy codeThe Code is as follows:
<? Php
Phpinfo ();
?>

Reference PHP predefined Constants
Copy codeThe Code is as follows:
<? Php
Echo $ _ SERVER ["SERVER_NAME"]; // localhost
Echo '<br/> ';
Echo $ _ SERVER ["SERVER_PORT"]; // 8090
Echo '<br/> ';
Echo $ _ SERVER ["DOCUMENT_ROOT"]; // D:/AppServ/www
Echo '<br/> ';
?>

V. Access form variables
Three Common Methods
Copy codeThe Code is as follows:
<? Php
Echo $ username; // short style. It is easy to confuse with variable names and is not recommended.
Echo '<br/> ';
Echo $ _ POST ['username']; // medium style, supported after version 4.1.0, recommended
Echo '<br/> ';
Echo $ HTTP_POST_VARS ['username']; // lengthy style, out of date, may be removed in the future
?>

Posttest.html
Copy codeThe Code is as follows:
<! DOCTYPE html PUBLIC "-// W3C // dtd html 4.01 Transitional // EN" "http://www.w3.org/TR/html4/loose.dtd">
<Html>
<Head>
<Meta http-equiv = "Content-Type" content = "text/html; charset = UTF-8">
<Title> method of obtaining form data </title>
</Head>
<Body>
<Form method = "POST" action = "demo10.php">
Username: <input type = "text" name = "username"/>
<Input type = "submit" value = "submit"/>
</Form>
</Body>
</Html>

6. String connection.
Copy codeThe Code is as follows:
<? Php
Echo "the student name is:". $ _ POST ['username'];
Echo "<br/> ";
Echo "welcome to". "school ";
?>