Introduction to photoshop learning PHP learning array courseware page 1/2

Subscript: The identification name in the array, which is the codename of the string or integer in the array. The array with several index values ​​is called a multi-dimensional array.
Index value: An index is a structure that sorts the values ​​of one or more columns in a database table.
Array classification
Arrays in PHP are divided into two types:
Indexed array: Indexed (indexed) index value is an integer, starting with 0. Indexed arrays are used when identifying things by position.
Associative array: Associative association uses a string as the index value, and the index value is the column name, and is used to access the column data.
Arrays are usually assigned values ​​
Generally, there are two ways to assign values ​​to arrays:
$a[1]="dsadsadsa";
$b[2]="dsadsadsad";
Use the array function:
$a=array ("dsads","dsadsa",321312);
One-dimensional array: When the array has only one index value (subscript), it is called a one-dimensional array.
Format of direct array assignment:
$Array variable name [index value] = data content;
Note: The index value can be a string or an integer, but 1 and "1" are different. One of them belongs to an integer and the other to a string. .
Arrays with the same name without index values ​​are arranged in order.
Example:
$a=array(1,2,3,4,5,6);
$b=array("one", "two", "three");
$c= array(0=>"aaa",1=>"bbb",2=>"ccc");
  $d=array("aaa",6=>"bbb","ccc");
    $e=array("name"=>"zhang", "age"=>20);
?>
    Two-dimensional array
The format of multi-dimensional array:
$a[0][]="dsadas ";
$a[0][]="dsadsa"; This group is 1 and 2 under the 0 index value under $a
If you use the array function to declare the format as follows:
$a=array("dsadsa"," dsadas",21,array("dsadsa","dsadas"));
Array traversal
foreach loop structure:
foreach only uses two formats: array loop
foreach(array_exprssion(array expression) as $value);
foreach(array_exprssion(array expression) as $key=>$value);
The first format traverses the given array_exprssion array. Each time through the loop the current value is assigned to my $calue and the pointer inside the array moves forward one step.
The second format does the same thing, except that the key value of the current cell will also be assigned to the variable $key in each loop.
When foreach starts executing, the pointer inside the array will automatically point to the first unit. Also note that foreach operates on a copy of the specified array, not the array itself
$arr=array(10,20,30,40,50,60);
foreach($arr as $k=>$v ){
echo "$k=>$v
";
}
Output result: 0=>10 1=>20 2=>30 3=>40 4=>50 5= >60//Subscript=>Integer
Combining list(), each() and while loop
each():
$arr=array(1,2,3,4,5);
$a= each($arr);
print_r($a);
Output result: Array ( [1] => 1 [value] => 1 [0] => 0 [key] => 0 )
Get Get the first value of the array value subscript key
list():
$arr3=array("a","b","c");
list($key,$value)=each($arr3) ;
echo $key."
".$value;
Output result: 0 a List() can be said to assign values ​​to a set of variables in one step. It can only be used for numerically indexed arrays and assumes that the numerical index starts from 0 start.
while loop
$arr=array(1,2,3,4,5,6,7,8,9,);
while(list($key,$value)=each($arr)){
$ key++;
echo $key."=>".$value;
echo "
";
}
echo "
";
Output result: 1=>1 2=>2 3=>3 4=>4 5=>5 6=>6 7=>7 8=>8 9=>9
reset() array pointer redirection
After executing each() , the array pointer will stay at the next element in the array or at the last element when the end of the array is reached.
is_array detects whether the variable is an array and returns true or false.
$arr=array(1,2,3,4,5,6,"saas");
while(list($k,$v) = each($ arr))
{
if(is_array($arr))
{
$x += $v;
echo $x;
}
else
{
$ x += $k;
}
}
This example It cannot fully reflect the function of is_array, but it can be used as a reference.
The pointer of the array
next(): responsible for moving the pointer backward
prve(): responsible for moving the pointer forward
end(): will point the pointer to the last element of the array
reset(): unconditionally move the current pointer to The first index position
Syntax format: mixed next(array name)
$arr=(array(1,2,3,4,5));
echo end($arr);
Output result: 5
key( ), current() and count()
key() function is to read the index value of the data pointed to by the current pointer.
The current() function reads the content data of the data pointed to by the current pointer. The
count() function is used to count the number of all elements in the array, which means that the function will return the length value of the target array.
Format: int count (array name);
key(): Get the key name from the associative array
$array = array('fruit1' => 'apple','fruit2' => 'orange','fruit3 ' => 'grape','fruit4' => 'apple','fruit5' => 'apple');
while ($fruit_name = current($array)) {
if ($fruit_name == ' apple') {
echo key($array).'
';
next($array);
}
Output result: fruit1,fruit4,fruit5
current(): Returns the value in the array Current unit
$transport = array('foot', 'bike', 'car', 'plane');
$mode = current($transport); // $mode = 'foot';
$mode = next( $transport); // $mode = 'bike';
$mode = current($transport); // $mode = 'bike';
$mode = prev($transport); // $mode = 'foot' ;
$mode = end($transport); // $mode = 'plane';
$mode = current($transport); // $mode = 'plane';
Pay attention to the example to return the current unit in the array
count(): Calculate the number of units in the array
$arr=array(1,2,3,4,5,6);
echo count($arr);
Output result: 6
array_change_key_case()
array_change_key_case returns An array whose string key names are all lowercase or uppercase contains two morphological functions: [CASE_UPPER] to convert to uppercase, and [CAS_LOWER] to convert to lowercase.
$input_array = array("FirSt" => 1, "SecOnd" => 4);
print_r(array_change_key_case($input_array, CASE_UPPER));
Output result: Array ( [FIRST] => 1 [SECOND ] => 4)
 array_chunk() The
array_chunk() sub-function will decompose the data content of the target array into several small arrays with the specified number of indexes and include them in the original array.
$arr=array(1,2,3,4,5,6);
$a=array_chunk($arr,3);
print_r($a);
Output result: Array ( [0] => Array ( [0] => 1 [1] => 2 [2] => 3 ) [1] => Array ( [0] => 4 [1] => 5 [2] = > 6 ) )
It is equal to dividing the sum of the number of array units by 3
array_count_values ​​
array_count_values ​​is used to calculate the number of occurrences of each value in the target array
Syntax format: array_count_values ​​(target array)
The result returned by this function The value will be expressed in the form of an array using the content data of the original array as an index.
$arr=array(1,2,3,3,2,6);
print_r(array_count_values($arr));
Output result: Array ( [1] => 1 [2] => 2 [ 3] => 2 [6] => 1)

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