With "Mini C# Pro" you can write and compile C# code on your Android device.
This app has the same functionality as my free app "Mini C#". However "Mini C# Pro" also offers syntax highlighting. Some possible extra useful features I might add in the future are: full-screen-mode, custom-keyboard, some feature to facilitate bug-finding.
As all paid apps in the Play Store there is a 15 minute window to try out the app for free. In these 15 minutes you can cancel your purchase and reclaim your money.