A summary of how to use PHP arrays

An array is a collection of data that organizes a series of data to form an operable whole. Each entity of an array contains two items: a key and a value.

1. What is an array
An array is a collection of data that organizes a series of data to form an operable whole. Each entity of an array contains two items: a key and a value.
2. Declaring data
There are two main ways to declare an array in PHP:
First, use the array() function to declare an array,
One is to directly assign values ​​ to array elements. Feifei Asp! Technology Park
array() function declares the array in the array([mixed...]) format. The syntax of the mixed parameter is key=>value
For example,

$array=array("1"=>"Editor","2"=>"Cheng ","3"=>"Word","4"=>"Dictionary");
print_r($array);
echo "
";
echo $array[ 1]; //Note: The subscript starts from 0 by default
echo $array[2];
echo $array[3];
echo $array[4];
?>

Assign values ​​to array elements directly.
If you do not know the size of the array when you create it, or the size of the array may change when you actually write the program, it is better to use this method of array creation.
For example,

$array[1]="I";
$array[2]="love";
$array[3]="PHP";
print_r($array); //Output the structure of the created array
?>

3. Types of arrays
PHP supports two types of arrays:indexed arrayandassociative array,the former uses numbers As keys, the latter uses strings as keys.
4. Output Array
Outputting array elements in PHP can be achieved through the echo and print statements, but this can only be done for Output an element in the array; to output the array structure, use the print_r() function, its syntax: print_r(mixed expression),The parameter expression is an ordinary integer or character Type or real type variable outputs the variable itself. If the parameter is an array, all elements in the array are displayed in the order of a certain key value and elements.
5. Array construction
One-dimensional array:
When the elements of an array are variables, it is called a one-dimensional array. Feifei As.p Technology Park
Declare a one-bit array: Type specifier array name [constant expression];
Two-dimensional array:
When a When the element of the array is a one-bit array, it is called a two-dimensional array.
For example,

$str = array (
"Network Programming Language"=>array ("PHP","JSP", "ASP"),
"Sports"=>array ("m"=>"Football","n"=>"Basketball"));
print_r ( $str) ;
?>

6. Traversing the array
Traversing all the elements in the array is a common operation, and the query can be completed during the traversal process or other functions. There are many ways to traverse an array in PHP. The two most commonly used methods are introduced below.
Use the foreach structure to traverse the array;
Use the list() function to traverse the array. The list() function can only be used for numerically indexed arrays, and the numerical index starts from 0. .
Example: Use list() and each() to authenticate user login:

//Output user login information
while(list($name,$value)=each($_POST)){
if($name!=" submit"){
echo "$name=$value
";
}
}
?>

7. Count the number of elements in an array
In PHP, use the count() function to count the number of elements in the array. The syntax is: int coun(mixed array[,int mode]), The parameter array is a required parameter and mode is an optional parameter. If COUNT——RECURSIVE (or 1) is selected, this function will recursively pair the array array. For example,

##$array = array("php" => array("PHP Function Reference Collection", "PHP Program Development Example Collection"," PHP Database System Development Complete Manual"),
"asp" => array("ASP Experience and Skills Collection")
); //Declare a two-dimensional array
echo count($array,COUNT_RECURSIVE) ;//Recursively count the number of array elements, the running result is 6
?>

#8. Array sorting
< ;1>Use sort() and rsort() to sort the array in ascending and descending order respectively, for example,
$array=array(5,26,37,18,9,42 ,88,66);
$array1=sort($array);
for($i=0;$iecho $array[$i ]." ";
}
echo "
";
$array1=rsort($array);
for($i=0;$iecho $array[$i]." ";
}
?>
Running results:
5 9 18 26 37 42 66 88
88 66 42 37 26 18 9 5

Use ksort() and asort() to sort the associative array
If an associative array is used, the key and sum must be maintained after sorting The values ​​are sorted in the same order. This requires the use of ksort() and asort() functions, such as, $array=array('php'=>1,'jsp '=>2,'asp'=>3);
ksort($array);
print_r($array);
echo "
";
asort($ array);
print_r($array);
?>
Run result:
Array ( [asp] => 3 [jsp] => 2 [php] => 1 )
Array ( [php] => 1 [jsp] => 2 [asp] => 3 )

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