Check Input Function Written In PHP

Please ONLY bid if you know what a function is: I need someone to write a function in PHP. My website allows users to enter and change data. They can change their password, description, etc. So I will need a function to check their input to make sure they do not try to put in harmful code. I will call this function as follows: $result = checkinput($string, $type); The $string is the string to be checked and $type is the type of this string. There can be 4 different types of strings. You might want to use a switch statement inside this function to handle the different types. The types I need this function to handle: 1. password: (this string can only be alpha numeric from 3 to 15 characters long, return error if bad) 2. email: (just check to make sure this appears to be a valid email address, we don't really have to validate it. error if bad) 3. url link: (only allow what has to be in a url link, and just error if something else is here that should not be. also return the leading http:// in case they don't have this in their string) 4. description: (this covers everything else. i don't want any code in this that might be harmful such as html, php, java etc. you might want to just cover the things that we allow rather than what we dont. we do want to allow certain characters like ' & / and others needed for description, etc.) On the description you can just take out what we don't allow and leave the rest. Example: Hello, I have been very <b>busy</b> today. function returns: Hello, I have been very busy today. If you do need to return an error return the following in the $string. 'ERRBDSTR' Just ask if there is something about this project that you do not understand.