how recursion work in php code example

Example 1: recursive function in php

<?php    
function factorial($n)    
{    
    if ($n < 0)    
        return -1; /*Wrong value*/    
    if ($n == 0)    
        return 1; /*Terminating condition*/    
    return ($n * factorial ($n -1));    
}    
    
echo factorial(5);    
?>

Example 2: recursive function in php

<?php    
function display($number) {    
    if($number<=5){    
     echo "$number <br/>";    
     display($number+1);    
    }  
}    
    
display(1);    
?>