Summary of PHP array declaration, traversal, and array global variable usage_PHP tutorial

PHP tutorial: array declaration, traversal, array global variables

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/*
* 1. Overview of arrays
* 1. The essence of arrays: manage and operate a set of variables, batch processing
* 2. Arrays Composite type (can store multiple)
* 3. Arrays can store data of any length and any type of data
* 4. Arrays can complete the functions of other language data structures (linked lists, queues , stack, collection class)
*
*
*
* 2. Classification of arrays
* There are multiple units in the array, (units are called elements)
* Each Element (subscript [key] and value)
* When accessing an element individually, the element is accessed through the subscript (key)
* 1. One-dimensional array, two-dimensional array, three-dimensional array. . . Multidimensional array
* (an array of arrays means that other arrays are stored in the array)
* 2. There are two types of arrays in PHP
* Index array: It is an index whose subscript is a sequential integer
* Associative array: The subscript is a string as an index
*
* There are only two types of subscripts (integer, string)
*
*
* 3. Multiple arrays Declaration method
*
* 1. Directly assign a value to the array element declaration
* If the index subscript is not given, the sequential index will start from 0
* If the index subscript is given, the next It will increase by 1 starting from the largest
* If the previous subscript appears later, if it is an assignment, the previous element will be reassigned
* When mixed declaration, index and association do not affect each other (it does not affect the index subscript) Declaration)
*
* 2. Use the array() function to declare
* The default is an index array
* If you specify a subscript for an associative array and an index array, use key => value
* Use " , " to split
* between multiple members. 3. Use other function declarations
*
*
*
*
*/
//Index array
$user[0]=1;//User serial number
$user[1]="zhangsan";//User name
$user[2]=10;//Age
$ user[3]="nan";//Gender
echo '

'; <br>print_r($user); <br>echo '

';
//Association Array
$user["id"]=1;
$user["name"]="zhangsan";
$user["age"]=10;
$user["sex "];
$user["age"]=90;//Assignment
echo $user["name"];//Output
//Use array() to declare the array
$user =array(1,"zhangsan",10,"nan");
//Use array() to declare an associative array
$user=array("id"=>1,"name"=> "zhangsan","age"=>10,"sex"=>"nan");
//Declare a multi-dimensional array (multiple records) to save multiple user information records in a table
$user=array(
//Use $user[0] to call this line, such as calling the name in this record, $user[0][1]
array(1,"zhangsan",10 ,"nan"),
//Use $user[1] to call this line, such as calling the name in this record, $user[1][1]
array(2,"lisi",20 ,"nv")
);
//Array saves multiple tables, each table has multiple records
$info=array(
"user"=>array(
array(1,"zhangsan",10,"nan"),
array(2,"lisi",20,"nv")
),
"score"=>array(
array(1,90,80,70),
array(2,60,40,70)
)

);
echo $info["score"][1 ][1];//Output 60,
?>
Array super global variable
/* Predefined array:
* Automatic global variable---super Global array
*
* 1. Contains data from the WEB server, client, operating environment and user input
* 2. These arrays are special
* 3. Automatically take effect in the global scope, These arrays can be used directly
* 4. Users cannot customize these arrays, but the operations of these arrays are the same as those defined by themselves
* 5. These arrays can be used directly in functions
*
* $_GET //Variables submitted to the script via URL request
* $_POST //Variables submitted to the script via HTTP POST method
* $_REQUEST //Via GET, POST and COOKIE mechanisms Variables submitted to the script
* $_FILES //Variables submitted to the script via http post method file upload
* $_COOKIE
* $_SESSION
* $_ENV //Execution environment submitted to the script Variables
* $_SERVER //Variables are set by the WEB server, or directly associated with the execution environment of the current script
* $GLOBALS //As long as the variables that are valid for the current script are here, the keys of the array The name of the global script
*
*
*/
//Super global array can be called directly inside the function
$arr=array(10,20);//General array
$_GET=array(50,90);//Super global array
function demo(){
global $arr;//When calling global variables, you must first include
print_r($arr);
print_r($_GET);//Directly call the super global array without including
}



?>

//Use the passed value directly as a variable. Useful when register_global=on in the php.ini configuration file.
echo $username."
";
echo $email."
";
echo $page."
";
//The most stable Value method
echo $_GET["username"]."
";
echo $_GET["email"]."
";
echo $_GET["page "]."
";
?>
this is a $_GET test

username:

password:< ;input type="password" name="pass" />



< ;/form>
print_r($_GET);//Cannot receive
print_r($_POST);//This is how to receive
?>
< ;?php
//Usage of $_ENV
echo'

'; <br>print_r($_ENV); <br>echo'

';
//Display Current environment
// You can also traverse individually
?>
//Use the $GLOBALS super-global array to call global variables inside the function
$a=100;
$b=200;
$c=300;
function demo()
{
//Directly call global variables
echo $GLOBALS["a"]."";
echo $GLOABLS["b"]."
";
echo $GLOABLS["c"]."
";

}
?>

Array traversal
/* Array traversal
*
* 1. Use the for statement to loop through the array
* 1. Other languages ​​(only this method)
* 2. This method is not the preferred method in PHP
* 3. The array must be an indexed array, and the subscripts must be consecutive.
* (index array subscripts can be discontinuous, arrays and associative arrays, these two cannot be traversed)
*
* 2. Use the foreach statement to loop through the array
* foreacho(array variable as Variable value) {
* // Loop body
* }
* 1. The number of loops is determined by the number of elements in the array
* 2. Each loop will assign the elements in the array to Later variables
*
* foreach (array variable as subscript variable => value variable) {
* }
*
*
* 3.while() list() each() combines a loop to traverse the array
*
* each() function:
* 1. Requires an array as a parameter
* 2. Returns an array
* 3. Returns The returned array has four subscripts (fixed): 0, 1, key, and value.
* 0 and the key subscript are the keys of the current parameter array element.
* 1 and the value subscript are the keys of the current parameter array element. Value
* 4. By default, the current element is the first element
* 5. Each time it is executed, the current element will be moved backward
* 6. If this function is executed again at the last element, then Return false
* list() function:
* 1. list()=array(); an array needs to be assigned to this function
* 2. The number of elements in the array must be the same as list( ) The number of parameters in the function is the same
* 3. Each element value in the array will be assigned to each parameter in the list() function, and list() will convert each parameter into a variable
* 4.list () can only accept index arrays
* 5. Assign values ​​to parameters in the order of index subscripts
*
*
*
*/
//for statement traverses the array
$user=array(1,"zhangsan",40,"nan");
for($i=0;$i{
echo"$user[ {$i}]=".$user[$i]."
";
}

//Use foreach
$user=array(1,"zhangsan", 40,"nan");
foreach($user as $val)//$val is a custom variable
{
echo $val."
";//Output and subscript Irrelevant
}
foreach($user as $key=>$val)//$val $key are all custom variables
{
echo $key."=====> ;".$val."
";
}

//foreach traverses multi-dimensional arrays
$info=array(
"user"=>array(
//$user[0]
array(1, "zansan", 10, "nan"),
//$user[1][1]
array(2, "lisi", 20, "nv"), //$user[1]
//$user[2]
array(3, "wangwu", 30, "nan")
),
" score"=>array(
array(1, 100, 90, 80),
array(2, 99, 88, 11),
array(3, 10, 50, 88)
),
"connect"=>array(
array(1, '110', 'aaa@bbb.com'),
array(2, '120', 'bbb@ccc. com'),
array(3, '119', 'ccc@ddd.com')
)
);
foreach($info as $tableName=>$table)
{
echo '';
echo '';
foreach($table as $row)
{
echo '';
foreach($row as $col)
{
echo '';
}
echo '';
}
echo '';
}

//Usage of each()
$user=array("id"=>1,"name"=>"zhangsan","age "=>10,"sex"=>"nan");
$a=each($user);//Array ( [1] => 1 [value] => 1 [0] => id [key] => id ) Default is the value of the first element
print_r($a);
$b=each($user);
print_r($b); //Array ( [1] => zhangsan [value] => zhangsan [0] => name [key] => name ) Each time it is executed, traverse backward one

$c= each($user);
print_r($c);//Array ( [1] => 10 [value] => 10 [0] => age [key] => age )
$d=each($user);
print_r($d);//Array ( [1] => nan [value] => nan [0] => sex [key] => sex )
$e=each($user);
var_dump($e);//bool(false) When there is no element, the value returned
//each() cooperates with while traversal
$user=array("id"=>1,"name"=>"zhangsan","age"=>10,"sex"=>"nan");
while($arr =each($user))
{
//echo $arr[0]."====>".$arr[1]."
";//pass 0, 1 to display the key (subscript) and value
echo $arr["key"]."===>".$arr["value"]."
";//By key, value to display the key value
}

//Usage of list() function
list($name,$age,$sex)=array("zhangsan",10,"nnnnn");
echo $name."
";
echo $age."
";
echo $sex."
";
//Another way to use it
list(, ,$sex)=array("zhangsan",10,"nnnnn");
echo $sex."
";//Only convert gender into variables
//ip judgment
$ip="192.168.1.128";
list(,,,$d)=explode(".",$ip);//explode means separated by . and returns an array
echo $d ;//Get out 128
//List() can only receive examples of index arrays
$user=array("id"=>1,"name"=>"zhangsan","age"= >10,"sex"=>"nan");
list($key,$value)=each($user);//Array( [1]=>1 [0]=> id) assign values ​​to the parameters in the list in order of index subscript, so first the 0 key and then the 1 value
echo $key."--->".$value;
//while list() each () Use in combination
$user=array("id"=>1,"name"=>"zhangsan","age"=>10,"sex"=>"nan");
while(list($key,$value)=each($user))
{
echo $key."--->".$value."
";
}

//Solution to display only once in multiple loops
//Use the internal pointer control function of the array
//next(array); the array pointer moves to the next
//prev(array); the array pointer moves to the previous one
//reset(array); the array pointer moves to the first one (reset)
//end(array); the array pointer moves to the last one
//current(array); Get the value of the current element, which is the element pointed to by the array pointer.
//key(array); Get the key value (subscript) of the current element
$user=array("id"=>1,"name"=>"zhangsan","age"= >10,"sex"=>"nan");
while(list($key,$value)=each($user))
{
echo $key."--- >".$value."
";
}
//Move the array pointer here to the first one and the following loop will output
//reset($user)
while(list($key,$value)=each($user))//Because each() returns false to the last one, the loop jumps out directly
{
echo $key."---> ;".$value."
";
}
while(list($key,$value)=each($user))//Because each() returns false to the last one, so The loop jumps out directly
{
echo $key."--->".$value."
";
}

echo current($user)." =====>".key($user);
?>

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