Question

the only thing i know about this subject is…

in PHP 5, when a variable used without assigned any value, then it a warning will be shown.

Is there any other difference between this 2 different version ?

Answer 1

There is no general difference between variables in PHP 4 and 5.

What you are probably referring to is the ´E_NOTICE` error reporting level. When that level is turned on, PHP will complain if a variable is used that hasn’t been assigned yet. That level existed in PHP 4 already:

// Report all errors except E_NOTICE
// This is the default value set in php.ini

error_reporting(E_ALL ^ E_NOTICE);

echo $hello_world;  // Will output nothing, but also not output a notice

error_reporting(E_ALL);

echo $hello_word;   // Will output "Notice: Undefined variable"

PHP’s error reporting can be influenced through the “error_reporting” php.ini setting, or during runtime of the script using the error_reporting() function.

As for other differences, there’s a load of them. Check out Gordon’s link about Migrating from PHP 4 to 5.