This is a very interesting tutorial if you would like to build your own calculator written in PHP. It guides you through all the steps and it is very clean written and has a good error checking. It uses if, witch and other math functions.

Like in all programing languages, PHP too has math functions. The difference with other programing languages is that PHP is one of the best to recognize variables as numeric without previously define them as so. This is what you will learn in this www.thenewboston.com video tutorial.