Recursive Functions are functions that auto-call themself. Generally, a recursive function returns a value that are passed as argument, so the value is passed from an auto-call to the other, until it is returned.
Recursive functions are very useful in equations with factorial numbers and some operatios with multi-dimensional array.
Factorials are written like 6! and this means: 6 * 5 * 4 * 3 * 2 * 1. So 6! is 4320 and 4! is 24.
In the fallowing example we have a recursive function that finds the factorial of a number "$nr" (here 8).

// this function auto-calls itself (decrementing $nr) until $nr is 0
function factorial($nr) {
  if($nr > 0) $re = $nr * factorial($nr-1);
  else if($nr == 0) $re = 1;

  return $re;

echo '8 factorial is: '. factorial(8);        // 8 factorial is: 45360

- To see another example, visit this page: Get all the unique numbers from two-dimensional array.

Daily Test with Code Example

Which tag is used to add lists into <ul> and <ol> elements?
<dt> <dd> <li>
Which value of the "display" property creates a block box for the content and ads a bullet marker?
block list-item inline-block
.some_class {
  display: list-item;
Which instruction converts a JavaScript object into a JSON string.
JSON.parse() JSON.stringify eval()
var obj = {
 "courses": ["php", "javascript", "ajax"]
var jsonstr = JSON.stringify(obj);
alert(jsonstr);    // {"courses":["php","javascript","ajax"]}
Indicate the PHP class used to work with HTML and XML content in PHP.
stdClass PDO DOMDocument
$strhtml = '<body><div id="dv1"></div></body>';
$dochtml = new DOMDocument();
$elm = $dochtml->getElementById("dv1");
echo $elm->nodeValue;    //
Recursive Functions in PHP

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