This is a complete tutorial, discussing how to build a simple calculator app for Android. Check it out, and implement some of the recommended improvements.

You'll start with the basics, learning to build basic apps in Android Studio using Kotlin. You'll learn the fundamentals, then discover layouts and views to design the app you want.

Find out what to look for in the latest version of Android Studio, including support for Kotlin, Java 8, and a wealth of new tools and plugins. If you’re new to Android Studio, this tutorial ...

The Windows Calculator is now open source, and the folks at Uno Platform took the source code and put it onto Android.