PHP and MYSQL Programming [Fourth Edition] Chapter 3 Essay - (2), MySQL Programming

Chapter 3 PHP Basics

（3.6——3.11）

3.6 Variables

Variable declaration

Variable assignment: assignment by value/assignment by reference

Variable scope:

Local variables: Variables declared in a function can only be referenced in the function

Function parameters: Any function that accepts parameters must declare these parameters at the beginning of the function. Although these parameters accept values from outside the function, they are no longer accessible after exiting the function

Parameter instance PHP and MYSQL Programming [Fourth Edition] Chapter 3 Essay - (2), MySQL Programming_PHP Tutorial

//Multiply a value by 10 and return it to the caller function x10 ($value){ $value = $value * 10; return $value; } //The parameters will be revoked after the function is executed

Global variables: (use with caution)

When accessing within a function, just add the keyword global

in front of the variable

Another way is to use PHP’s $GLOBALS array. $GLOBALS[""];

Static variable:

Unlike variables declared as function parameters, function parameters will be revoked when the function exits, while static variables will not lose their value when the function exits, and can also save this value for use when calling this function again

You can declare a static variable by adding the keyword STATIC in front of the variable name

PHP super global variables:

You can obtain detailed information about the current user session, user operating environment and local operating environment through PHP's super global variables

foreach ($_SERVER as $var => $value) { echo "$var => $value
"; } //For example, display the user IP address: printf("Your IP address is: %s",$_SERVER['REMOTE_ADDR']); //You can also get information about the user's browser and operating system: printf("Your browser is: %s",$_SERVER['HTTP_USER-AGENT']); Gives all predefined variable codes related to the given web server and script execution environment

Use the GET method to obtain the passed variables

Use the POST method to get the passed variables

Get information stored in cookies:

The $_COOKIE super global variable stores the information passed to the script through the HTTP cookie

These cookies are generally set by a previously executed PHP script through the PHP function setcookie()

Use POST method to get information about uploaded files

The $_FILES super global variable includes information about the data uploaded to the server through the POST method

$_FILES is a two-dimensional array containing 5 elements:

$_FILES['upload-name']['name']. The file name of the file uploaded from the client to the server

$_FILES['upload-name']['type']. The MIME type of the uploaded file. Whether this variable is assigned a value depends on the browser's capabilities

$_FILES['upload-name']['size']. Size of uploaded file in bytes

$_FILES['upload-name']['tmp_name']. After uploading, give this file a temporary name before moving it to its final location

$_FILES['upload-name']['error']. Upload status code. 5 possible values:

UPLOAD_ERR_OK. File uploaded successfully

UPLOAD_ERR_INI_SIZE. The file size exceeds the maximum value set by the upload_max_filesize directive

UPLOAD_ERR_FORM_SIZE. File size exceeds the maximum value specified by the MAX_FILE_SIZE hidden form field parameter (optional)

UPLOAD_ERR_PARTIAL. Only part of the file was uploaded

UPLOAD_NO_FILES. No file specified in file form

More about the operating system environment:

The $_ENV super global variable provides information about the server environment where the PHP parser is located

$_ENV['HOSTNAME']. Server hostname

$_ENV['SHELL']. System shell

Get information stored in the session: $_SESSION super global variable contains information related to all session variables

Variable of variable: Add a dollar sign before the original variable name, and then assign another value to it

3.7 Constants

Constants refer to values that cannot be modified in the program

The define() function defines a constant by assigning a value to a variable name. Its form is as follows:

boolean define(string name,mixed value [,bol case_insensitive])

If the optional parameter case_insensitive is used and the value of this parameter is TRUE, then subsequent references to this constant will not be case sensitive

There is no need to use the dollar sign before constants

Once defined, a defined constant cannot be redefined or undefined.

3.8 Expression

Operand (operand): The operand is the input of the expression

Operator: An operator is a symbol that specifies an action in an expression

Operator list

Operator precedence

Operator associativity

Arithmetic operators: " ", "-", "*", "/", "%"

Assignment operators: "=", " =", "*=", "/=", ".="

String operators: "=", ".="

Self-increase and self-reduced operator: "", "-"

According to the placement position of the auto-increment and auto-decrement operators, they can be divided into front auto-increment operation, front auto-decrement operation, post-increment operation, and post-auto-decrement operation

Logical operators: "&&", "AND", "||", "OR", "!", "NOT", "XOR"

Equality operators: "==", "!=", "==="

Comparison operators: "<", ">", "<=", ">=", "($a == 12) ? 5 : -1" (if $a is equal to 12, Return value 5; otherwise return value -1)

Bit operators: "&", "|", "^" (XOR. Every bit contained in $a or $b is XORed), "~ $b" (not. Every bit in $b) Bit opposite), "$a<<$b" (shift left. Move $a's bit left by $b steps), ">>" (shift right)

3.9 String insertion

Double quotes

Escape sequence: Description

n Line break character

t Horizontal tab

Backslash

single quote

Braces

heredoc syntax:

php

echo <<<EXCERPT

The homepage of the blog park (i.e. the homepage of the website) can only publish original, high-quality content that readers can learn from.

EXCERPT; ?> //The start and end identifiers must be the same. The start and end identifiers here are EXCERPT, which can also be customized //The start and end identifiers can only consist of alphanumeric characters and underscores, and cannot start with numbers or underscores //There must be 3 angle brackets before the start identifier:<<< //The end identifier must be at the beginning of a line and cannot be preceded by any spaces or other extra characters. //Any spaces after the start and end identifiers will cause a syntax error heredoc example Nowdoc syntax

3.10 Control Structure

Conditional statements (the syntax of each statement is omitted)

if statement

else statement

elseif statement

switch statement

Loop statements (the syntax of each statement is omitted)

while statement

do...while statement

for statement

foreach statement

Break statement and goto statement