Normally I would be crazy for writing something like this. A PHP calculator is not exactly an efficient calculator. PHP is a great language, but not exactly for this type of application. Especially when any real operating system already has a much better calculator that comes installed by default. The real purpose of this was to begin learing the PHP language. Enjoy, and please let me know if you see any bugs. If you want to look at the code, you can download it here. While it's nothing spectacular, someone new at this might learn something.