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).

```<?php
// 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

##### PHP-MySQL
Which tag adds a new line into a paragraph?
<b> <br> <p>
```First line ...<br>
Other line...```
Which CSS property can be used to add space between letters?
text-size word-spacing letter-spacing
```#id {
letter-spacing: 2px;
}```
What JavaScript function can be used to get access to HTML element with a specified ID?
getElementById() getElementsByTagName() createElement()
```var elm = document.getElementById("theID");
var content = elm.innerHTML;
alert(content);```
Click on the "echo" correct instruction.
echo "CoursesWeb.net" echo "CoursesWeb.net"; echo ""CoursesWeb.net";
`echo "Address URL: http://CoursesWeb.net";`
Recursive Functions in PHP

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