PHP foreach() usage and examples, phpforeach_PHP tutorial

PHP foreach() usage and examples, phpforeach

Original URL:
http://blog.csdn.net/china_skag/article/details/6444727

PHP 4 introduced the foreach structure, which is very similar to Perl and other languages. This is just a convenient way to iterate over an array. foreach can only be used with arrays, and an error will occur when trying to use it with other data types or an uninitialized variable. There are two syntaxes, the second being a less important but useful extension of the first.

foreach (array_expression as $value)
statement

foreach (array_expression as $key => $value)
statement

First format traversal The given array_expression array. Each time through the loop, the value of the current cell is assigned to $value and the pointer inside the array is moved forward one step (so the next cell will be obtained in the next loop).

The second format does the same thing, except that the key name of the current cell is also assigned to the variable $key in each loop.



Let’s look at the first statement first. This statement is relatively simple. array_expression refers to an array expression. The as $val statement will sequentially obtain the value of the array and save it to $val. In variables, this method can only obtain the value in the array, but not the subscript index value of the array. For example:

$myArray=array("1"=>"val1","2"=>"val2","3"=>"val3");
foreach($ MyRray as $ value) {
Print ($ val. "");
}

The result will output: Val1 Val2 Val3

In addition to getting the value of the element in the array like the first format, the second format can also get the index value of the element and save it to the $key variable. If the index value of the array has not been manually set, Then return to the system default setting value,
Look at the positive example:

First look at a simple one-dimensional array:

$myArray=array("1"=>"val1 ","2"="val2","3"=>"val3");
foreach($myArray as $key=>$val) {
 ​ print($key."=> ".$val.";");
}

The program will output: 1=>val1;2=>val2;3=>val3;, let’s look at it next A more complicated two-dimensional array traversal, the program is as follows:

$myArray=array(
"1"=>array("11"=>"val11","12"=> "val12","13"=>"val13"),
"2"=>array("21"=>"val21","22"=>"val22","23"= >"val23"),
"3"=>array("31"=>"val31","32"=>"val32","33"=>"val33")
);
print("

");
foreach($myArray as $key=>$val) {
        print("
• ".$key."< ;/li>");
  if (is_array($val)) { //Determine whether the value of $val is an array, if so, enter the lower level traversal
  print("
  ") ;
  foreach($val as $key=>$val) {
  print("
  • ".$key."=>".$val."
  ") ;
                                                                                                                                                                      
  
  1
  11=>val11
  12=>val12
  13=>val13
  2
  21=>val2 1
  22=> val22
  23=>val23
  3
  31=>val31
  32=>val32
  33=>val33
  
  
  and< li> is a label, which displays a solid dot and a hollow dot.
  Since the above is a two-dimensional array, the $val value obtained after the first traversal will be an array, so I added a judgment to the traversal for second-level array traversal.
  
  
  
  
  Another example to solve the puzzle
  
  $a = array("1"=>"中文"," 2"=>"Math","3"=>"English");
  $b = array("1"=>"95","2"=>"99","3 "=>"92");
  foreach($a as $key=>$value){
  echo $value;
  echo $b[$key]."
  " ;
  }
  ?>
  
  The question is why do we use $b[$key] instead of $b[$value] to output the value in array $b?
  
  Why is this?
  
  $a = array("1"=>"Chinese","2"=>"Mathematics","3"=>"English");
  The above one is exactly the same as the one below
  
  $a[1]="Chinese";
  $a[2]="Mathematics"
  $a[3]="English"
  
  The array we output above is How is it output?
  
  It must be echo $a[1];
  
  right?
  
  If there is no doubt let’s continue! ! ! !
  
  
  ————————————————————————————————————————————
  
  
  Simply put foreach
  
  The format is like this foreach (array name as subscript => value)
  
  The subscript is the $a[1] above, and the 1 here is the subscript of the array mark!
  
  By now you should understand why $a[$key] is output like this
  
  Please remember that no matter how you change it, the output method of the array will always be $a[1], no It is $a['language']
  
  
  
  
  ============================ =====================================
  
  foreach() has two uses :
  1: foreach(array_name as $value){
  statement;
  }
  The array_name here is the name of the array you want to traverse. In each loop, the value of the current element of the array_name array is Assign to $value, and the subscript inside the array moves down one step, that is, the next loop will return to get the next element.
  
  
  2: foreach(array_name as $key => $value){                                                                                        , that is, in addition to assigning the value of the current element to $value, the key value of the current element will also be assigned to the variable $key in each loop. The key value can be a subscript value or a string. For example, "0" in book[0]=1, "id" in book[id]="001".
  
  
  
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  www.bkjia.comtruehttp: //www.bkjia.com/PHPjc/1010336.htmlTechArticlePHP foreach() usage and examples, phpforeach original website: http://blog.csdn.net/china_skag/ article/details/6444727 PHP 4 introduced the foreach construct, much like Perl and other languages. This...