If you have a background in C, then you're probably already familiar with the character type functions because that is where they come from (don't forget that PHP is actually written in C). But if you're into Python, then it's only fair to point out that the PHP Ctype functions have absolutely nothing to do with the Python's ctypes library. It's just one of those tragic and totally unavoidable naming similarities.

He briefly explains how the functions work and at least one "gotcha" to watch out for if you're using them for input validation. He then goes through the list of the eleven ctype functions and briefly describes what they do. Some example code is also included showing how you can use them to validate a value based on the true/false return from the function call.

In this article, we will be looking at user authentication. User authentication simply means verifying that a particular user has the right to access a part of our application. Because our application deals with user preferences, access control is even more pertinent especially since multiple users are going to try to access this application at any given time.

As a part of this user validation and customization, they need to create a form that non-human scripts have a harder time using (hopefully weeding them out and getting better user information). The article steps you through a few lines of code that you can use to create a simple image of a four-digit number whose value is placed in a session variable so it can be validated on submission of the form.