What are the advantages of a PHP5 over PHP4?

PHP5 has better support for classic object-oriented style programming. I’m sure there are other advantages, but that’s the one I’ve heard most. Of course, we’re onto something like 5.2 or 5.3 at this point, so if you’re still on PHP4 you should probably make the leap. AFAIK, you can keep programming in PHP4 style in PHP5. Upgrading would allow you to start working with the newer features as you are comfortable with them.

The object oriented features are great. It’s faster. It’s more secure. It will be supported longer (PHP 4 support will end soon I believe). And there are a new new useful functions.

OOP is better supported on PHP5, also they added few library such as mysqli, and few new functions, for example json_encode/decode

PHP 4 do not provide error handling this is the main advantage of PHP 5…