PHP Basics

One 、 Basic grammar

php Is a weak data type programming language , There is no need to define the type in advance , The data type of variable type and assignment related variable is not fixed 
   php  Variable name , Start with a letter or underscore , Cannot start with a number or a special character , Case sensitive .

   $a = 100;
   $a = “abc”;

	<?php
    	$a;
	    echo $a;
	?>

Running results ： Nothing out

php All integers in are signed

Can pass var_dump($changeThe\; amount1,$ Variable 2,…) Way to display its type
When it comes to computation , The data type will be converted to high precision

There is no output

Two 、 function

Can have no return value

Introduce other . php file

<?php
 	//1.
	require 'b.php';
 
	//2.  Introduce... Through variables 
	$fileName="b.php";
	require $fileName;
	
	//3.
	require ('b.php');
?>

57

12

3、 ... and 、 Array

When creating an array , There is no subscript assigned to an element ,php Will automatically use the current maximum subscript value ( Integers ), add 1 As a subscript to the element

If you give the same subscript to an element , The original value will be overwritten
As the index of the array ：true amount to 1,false amount to 0,null Equivalent to an empty string
Use decimals as key, Automatically truncate the decimal part
Arrays and objects cannot be used as key

// Use print_r To display the array 
	print_r($arr);
//var_dump Data types can be displayed when displaying arrays 
	var_dump($arr);

An error will be reported if the subscript is out of range when accessing the array

//php Arrays can grow dynamically 
    $a=array(2,3);
	$a[2]=56;
    echo $a[2];

Traverse ：

Four 、 Classes and objects

PHP The object is passed by reference

The address of the variable you want to pass in , Use &

Member functions （ Method ） No access modifier specified , The default is public
Member variables （ attribute ） The access modifier must be specified

php Member method ：

Example ：

Constructors ：





A class has and only has one construction method , stay php5 Although after __construct() and Class name () Can coexist , But in fact, only one can be used

The main function is to release resources , It's not destroying the object itself .
Before destroying the object , The system automatically calls the destructor method of this class
A class has at most one destructor method

Static variables can exist without creating objects , It is not a variable in the object , Is object independent , Static variables cannot be used this visit

Inherit ：
When creating a subclass object , By default, the constructor of its parent class will not be called automatically

If you need to access the methods of its parent class in a subclass , have access to Parent class :: Method name or parent:: Method name To complete

If you define multiple functions with the same name ( as follows ), An error will be reported at runtime ：

Methods cover :
① The number of parameters of subclass methods , Method name , It should be the same as the method of the parent class .
② A subclass method cannot reduce the access rights of a parent method

5、 ... and 、 other

1. Access database

Use mysql Extended library operations mysql Database steps ：

1、 stay mysql Create a library in the database , And create tables 、 Create data
2、 stay php Enabled in file mysql
3、 Establishing a connection
4、 Select database , Set character set , And send the sql
5、 Get data from the result set , Output to page
5、 Disconnect from database , Release related resources

mysqli The extension library is mysql An improved version of the extension library ,mysqli Extended library ratio mysql Expansion libraries are more efficient , Better stability
Use mysqli Extended library operations mysql Database i step ：

1、 stay mysql Create a library in the database , And create tables 、 Create data
2、 stay php Enabled in file mysqli expanded memory bank
4、 Establishing a connection
5、 Select database , send out sql
6、 From result set s Retrieve data from , Output to page
7、 Disconnect from database , Release related resources

2.MVC Development mode

MVC It's a design pattern , It forces the input of the application 、 Separate processing and output .
The application is divided into three core components ： Model 、 View 、 controller . They each deal with their own tasks

M Mainly by class To do it , Used to process specific business logic
V from php To do it , Mainly used to display data
C from php To do it , Used to respond to various requests of users

MVC advantage ：
Code readability 、 Expand 、 Maintenance enhancements
MVC The shortcomings of ：
Increased workload 、 Not suitable for small projects 、 It is more difficult to debug the program