[Fengma family _ php] basic php knowledge, _ basic php knowledge

[Fengma family _ php] basic php knowledge, _ basic php knowledge
Review

What is the development history of php and php?

Configure php in apache

Configure mysql in php

How apache works

How the web works (similar to 4)

Domain name-based VM configuration: httpd. conf loads httpd_vhost.conf and httpd_vhost.conf to configure the VM.

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PHP work

Php is a scripting language embedded in html code.

If the file does not use. if php ends, the apache file will not be handed over to php for processing, so the php code will be handed over to the browser intact, and the browser cannot parse the php code, so it will not output the final php code execution results

1. Embed php code in an html file

　　

2. Embed php code in html in the php File

　　　　

Note: apache will submit all files ending with. php to the php engine for processing. The php engine only processes php code and does not process other non-php code.

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Php independent files

No other code (html) is purely php code. (If you do not want to work with apache, you only need to use the php.exe file to run the PHP file.

　　

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Php basics php labels

1. Common labels

<? Php

// Php code

?>

Is the most common label Method

2. php script tag

<Script language = "php">

// Php code

</Script>

　　　　　　

Note: script labels are rarely used because they are easy to be confused with javascript labels.

3. Short tag

PHP does not support short labels by default. You need to set D: \ service \ php. ini in the configuration file.

<?

// Php code

?>

Effect

　　　　　

Note: by default, php does not support short tag syntax and must be enabled in the configuration file.

 

PHP comments

There are two types of php comments: Single-choice comments and block comments (multiple lines)

:#

Block comment/* Comment content */

PHP Variables

Variable naming rules

Variables in php are usually assigned values during definition.

Syntax Error

Weak Language

I. Use Variables

Use the variable directly. The precondition is that the current variable has been assigned a value (defined)

Output: echo $ variable name;

Judgment: if ($ variable name = 'value ')

　　　　　　

2. Modify Variables

Assign a new value to the original variable.

// Define variables

$ Age = 20

// Modify the variable

$ Age = 34

　　　　

Echo $ age // 34

 

3. delete variables

Release the value pointed to by the variable (release the variable itself)

Unset (variable name)

 

// Output released Variables

$ Age = 10;

Unset ($ age)

Echo $ age // error undefined

　　　　

Php Constants

Once defined, it cannot be modified. The 'quantity' that can only be used is called a constant.

　　　　

I. Syntax

Define ('constant name', constant value );

Ii. Common sense syntax 3: Use of constants

　　　　　　

Iv. Constant naming rule 5: Memory principle diagram of variables and constants

　　

6. How does the memory handle php script execution? 7. Note:

End symbol of the concluding sentence: English symbol;

Constant definition is loose than variable definition.

Suggestions on naming variables and constants

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Data Type

The data type is for various (variable) values, not for the variable itself

Floating Point Type

Timestamp

String

Double quotation marks

Concatenate two strings without spaces

Delimiters
Use a special symbol <to add a pair of start and end tags to include strings.

Definition of delimiters

Buddha: single quotes are more efficient than double quotes, because single quotes do not need to parse the variables and other content, as long as they are directly output.

Boolean

Composite data type

Special Data Types

Resource: all external data operations are called resource data.

Hexadecimal conversion

Conversion between binary, octal, decimal, and hexadecimal

System predefined Variables

The variables defined by the system are called pre-defined variables. There are nine pre-defined variables.

System predefined constantVariable

Get the value of a variable and use the value as a variable name to get the value of another variable.

That is, the value of the variable, as a variable of another value.

Pass Value

Value assignment between variables

Unset Principle

Swap variable value (both variables are integers)