This article is intended for the PHP programmer interested in avoiding some of the most common mistakes when applying PHP. The reader is expected to at least be familiar with PHP syntax, but should have a working knowledge of PHP functionality as well.

One of PHP's greatest strengths happens to be one of its greatest weaknesses as well: PHP is easy to learn. Many people are attracted to the language because of this, not realizing that it's a lot tougher to learn how to do it right.
There just hasn't been enough emphasis on good programming practice. Inexperienced coders are being asked to create and distribute complex web applications. Mistakes that an experienced programmer would avoid are all too common, such as the improper use of the printf() function or the misapplication of PHP's semantics.
In this three part article series, I present a list of 21 mistakes that I believe are frequently made and ranging in severity from non-critical down to those that can break the farm. I offer solutions, suggestions and/or comments on how to solve and prevent these errors, in addition to other tricks of the trade that I have gained over the years.