PHP - 递归函数

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

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);