The final project for my intro Java Programming class was to build a simple four-function calculator app for Android using Android Studio. In this project, we followed the Model-View-Controller architecture of design which separated the math processing from the physical display of the calculator itself. The calculator would round all answers to two decimal points as well as error check for infinity. The DEL key would also function as a sort of undo of the most recent key press by controlling a stack of inputs.
In hindsight, the lack of the traditional C, or clear, key was rather questionable!