Php Recursion Question

[ayaya]

<?
function f($a)
{
  if($a<2)
  {
 echo "before:".$a."</br>";
 f($a+1);
 echo  "after:".$a."</br>";
   }
}
f(0);
?>

 

Why the result is:

before:0

before:1

after:1

after:0

 

Can anyone help?

[trq]

Makes perfect sense to me. What exactly were you expecting?

[Jessica]

Your code basically does this:

call f(0);

echo before: 0

call f(1);

echo before: 1;

call f(2);

exit f(2)

echo after: 1;

exit f(1);

echo after: 0;

[ayaya]

exit f(2)

echo after: 1;

exit f(1);

echo after: 0;

 

Thank you for your help. But if exit f(2) and f(1), How comes the result after "afer"? I still don't understand it. Sorry I'm very stupid...

Edited January 1, 2013 by ayaya

[DavidAM]

Each invocation of the function is a separate occurance and gets its own local variables. The recursive call is NOT modifying $a. For that matter, you are not modifying it locally. If you want the recursive call to affect the local variable, you would have to pass by reference or return it:

 

function f($a)
{
  if($a<2)
  {
        echo "before:".$a."</br>";
        $a = f($a+1);
        echo  "after:".$a."</br>";
       }
  return $a;
}
f(0);