Is there a way to loop through a multidimensional array without knowing it's depth?

Yes, you can use recursion. Here's an example where you output all the elements in an array:

function printAll($a) {  if (!is_array($a)) {    echo $a, ' ';    return;  }  foreach($a as $v) {    printAll($v);  }}$array = array('hello',               array('world',                     '!',                     array('whats'),                     'up'),               array('?'));printAll($array);

What you should always remember when doing recursion is that you need a base case where you won't go any deeper.

I like to check for the base case before continuing the function. That's a common idiom, but is not strictly necessary. You can just as well check in the foreach loop if you should output or do a recursive call, but I often find the code to be harder to maintain that way.

The "distance" between your current input and the base case is called a variant and is an integer. The variant should be strictly decreasing in every recursive call. The variant in the previous example is the depth of $a. If you don't think about the variant you risk ending up with infinite recursions and eventually the script will die due to a stack overflow. It's not uncommon to document exactly what the variant is in a comment before recursive functions.

You can do the below function for loop-through-a-multidimensional-array-without-knowing-its-depth

// recursive function loop through the dimensional arrayfunction loop($array){    //loop each row of array    foreach($array as $key => $value)    {         //if the value is array, it will do the recursive         if(is_array($value) ) $array[$key] =  loop($array[$key]);         if(!is_array($value))          {            // you can do your algorithm here            // example:              $array[$key] = (string) $value; // cast value to string data type         }    }    return $array;}

by using above function, it will go through each of the multi dimensional array, below is the sample array you could pass to loop function :

 //array sample to pass to loop() function $data = [  'invoice' => [      'bill_information' => [          'price' => 200.00,          'quantity' => 5      ],      'price_per_quantity' => 50.00  ],  'user_id' => 20];// then you can pass it like this :$result = loop($data);var_dump($result);//it will convert all the value to string for this example purpose

You can use recursion for this problem:

Here is one example

$array = array(1 => array(1 => "a", 2 => array(1 => "b", 2 => "c", 3 => array(1 => "final value"))));//print_r($array);printAllValues($array);function printAllValues($arr) {    if(!is_array($arr)) {        echo '<br />' . $arr;        return;    }    foreach($arr as $k => $v) {        printAllValues($v);    }}

It will use recursion to loop through array

It will print like

abcfinal value