The first two digits represent red, the middle two digits represent green, and the last two digits represent blue.

Hexadecimal numbers include: 0123456789abcdef

Variables are defined starting with the $ symbol.

Rules for variable names: they must be composed of letters, numbers, and underscores, and cannot start with numbers.

unset(); //Delete the value and address of a variable from memory

empty(); //It is used to determine whether a variable is empty. If it is empty, it is True otherwise False.

isset(); //Used to determine whether a variable exists, True otherwise False

integer(int)

Floating point number (float/double)

boolean

string

array

object

resources

NULL

Converts to Boolean False in the following cases

In the following cases, it will be converted to numeric type

In the following cases, it will be converted to string type

settype(); Format: settype(variable to be converted, "conversion type");

Simply put the type you want to convert in parentheses, followed by the variable you want to convert. You need to use a new variable to receive the result after conversion!

For example: define("PI",3.14);

Use: echo PI;

Both logical AND and logical OR have a short-circuit effect. (short circuit AND and short circuit OR)

expression? true and false;

If you can't tell the difference, use invincible()

if(conditional expression){ Condition is established: go to this range }

if(conditional expression){ Condition is established: go to this range }else{ The condition is not true: move the interval }

if(conditional expression 1){ Condition 1 is true: go to this range }else if(conditional expression 2){ Condition 2 is established: go to this range }else if(conditional expression 3)……{ Condition 3 is established: go to this range }else{ If none of the above conditions are true, go to this range }

switch(variable){ case value 1: When the variable value is 1, the range to go break; case value 2: When the variable value is 2, the range to go break; … default: When all the above values ​​do not exist, the range to go break; }

if(conditional expression){ if(conditional expression 1){ if(conditional expression 2){ } } }

while(conditional expression){ If the condition is met, execute the code here }

do{ Give it a try first, then ask: Do you accept it? }while(conditional expression);

for(expression1;expression2;expression3){ When the condition is met, the code is executed }

Also called internal variables, they are variables declared inside a function. Their scope is limited to the inside of the function. It is illegal to use such variables after leaving the function. (Formal parameters are also local variables)

Also known as external variables, they are variables defined outside the function, and their scope ranges from the place where the variable is defined to the end of the program file.

Within the function, variables defined using the static keyword (static storage type)

Examples: var_dump(), is_bool(), is_string(), gettype()

Functions with regular parameters

Functions with pseudo-type parameters

Functions that reference parameters

function with default parameters

variadic function

Callback

recursive function

*$_SERVER server and execution environment information

*$_GET Array of variables passed to the current script via URL parameters.

*$_POST Array of variables passed to the current script via the HTTP POST method.

*$_FILES saves file upload information (detailed in the file processing chapter)

(Cookies and sessions are discussed in detail in the session tracking chapter)

*$_COOKIE An array of variables passed to the current script through HTTP Cookies (used to store login information for forums, libraries, blogs, etc.)

*$_SESSION An array of SESSION variables available to the current script. (Information storage for website shopping carts, etc.)

*$_REQUEST includes get, post and cookie

$_ENV stores system environment variable information

*$_SERVER["HTTP_REFERER"]--URL address of the previous page

--Host name of the server

*$_SERVER["SERVER_ADDR"]--The IP address of the server

$_SERVER["SERVER_PORT"]--server port

*$_SERVER["REMOTE_ADDR"]--Client IP

$_SERVER["DOCUMENT_ROOT"]--The web directory path of the server

*$_SERVER["REQUEST_URI"];//--URL address

echo $_GET["name"];

echo $_REQUEST["name"]; //Getting information will be slower than getting it above

*array_values ​​— Returns all values ​​in an array

array_keys — Returns all keys in an array

array_flip — swap keys and values ​​in an array

*in_array — Check whether a value exists in an array

array_reverse — Returns an array with the elements in reverse order

*is_array() -- determine whether it is an array

*count -- Count the number of cells in an array or the number of attributes in an object

array_count_values ​​-- Count the number of occurrences of all values ​​in the array

array_unique -- Remove duplicate values ​​from an array

array_filter -- Use a callback function to filter elements in an array

array_walk – applies a user function to each member of an array

array_map -- apply the callback function to the cells of the given array

*sort -- Sort the array (ascending order)

rsort -- sort an array in reverse order (descending order)

asort -- Sort an array while maintaining index relationships (associative array sorting)

arsort -- Sort an array in reverse order while maintaining index relationships

*usort – Sort values ​​in an array using a user-defined comparison function

uasort – Sort values ​​in an array using a user-defined comparison function and maintain index association

ksort -- Sort an array by key

krsort -- Sort an array in reverse order by key name

uksort -- Sort keys in an array using a user-defined comparison function

*natsort -- Sort an array using the "natural sorting" algorithm

natcasesort -- Sort an array in a case-insensitive manner using the "natural sort" algorithm

array_multisort – Sort multiple arrays or multidimensional arrays (understand)

array_slice -- remove a segment from an array

array_splice -- remove part of an array and replace it with another value

array_combine -- Create an array with the values ​​of one array as its keys and the values ​​of another array as its values

*array_merge -- merge one or more arrays

array_intersect -- Calculate the intersection of arrays

array_diff -- Calculate the difference of arrays