PHP Programming/foreach loop

From Wikibooks, open books for an open world
Jump to: navigation, search

Return to PHP.

The Code[edit]

foreach ($array as $someVar) {
  echo ($someVar . "<br />");
}

or:

foreach ($array as $key => $someVar) {
  echo ($key."holds the value ".$someVar."<br />");
}

Analysis[edit]

The foreach loop is a special form of the standard for loop. The example above will print all the values of $array. The foreach structure is a convenient way to loop through an array.

simple foreach statement[edit]

Foreach loops are useful when dealing with an array indexed with arbitrary keys (e.g. non-numeric ones):

$array = array(
  "1st" => "My House",
  "2nd" => "My Car",
  "3rd" => "My Lab"
);

To use the classical for structure, you'd have to write:

// get all the array keys
$arrayKeys = array_keys($array);
// get amount of values from array
$count = count($array);
// loop through the keys
for ($i=0; $i<$count; $i++) {
  // get each array value using its key
  echo $array[($arrayKeys[$i])] . "<br />";
}

Basically, an array value can be accessed only from its key: to make sure you get all the values, you first have to make a list of all the existings keys then grab all the corresponding values. The access to first aray value, the previous example does the following steps:

$firstKey = $arrayKeys[0]; // which is '1st'
$firstValue = $array[$firstKey]; // which is 'My House' ($array('1st'))

The foreach structure does all the groundwork for you:

foreach ($array as $someVar) {
   echo $someVar . "<br />";
}

Note how the latter example is easier to read (and write). Both will output:

My House
My Car
My Lab

foreach with key values[edit]

If you need to use the array's keys in the body of your loop, just add the variable as in the following statement. The phrase '$myKey => $value' makes the value of the key accessible:

foreach ($array as $myKey => $value) {
  // use $myKey
}

Note that this is very usefull when constructing a dropdown list in HTML. You can use a foreach-loop to have the $myKey variable inserted into the value="..." part and the $value as the actual text.

This form mimics the way we used custom keys for $array elements. It will not only assign the elements of $array to $someVar, but also assign the keys of those elements to $i.


Crystal Clear app terminal.png PHP Code:

<?php
$array = array("1st" => "My House", "2nd" => "My Car", "3rd" => "My Lab");
foreach ($array as $key => $someVar) {
  echo $key . ": " . $someVar . "<br />\n";
}
?>

Crystal Clear app kscreensaver.png PHP Output:

 1st: My House<br />
 2nd: My Car<br />
 3rd: My Lab<br />

Crystal 128 yast default.png HTML Render:

 1st: My House
 2nd: My Car
 3rd: My Lab


Note that if you change the assigned variable inside the foreach loop, the change will not be reflected to the array. Therefore if you need to change elements of the array you need to change them by using the array key. Example:

$array = array(
  "1st" => "My House",
  "2nd" => "My Car",
  "3rd" => "My Lab"
);
 
foreach ($array as $i => $someVar) {
 
  // OK
  if($someVar == 'My Lab')
    $array[$i] = 'My Laboratory';
 
  // doesn't update the array
  $someVar = 'Foo';
}