Hi,
I'm wondering if you have any tip for a good app to write some basic c# code in no graphic.
When I did use to run Windows I did use Notepad++ but as far as I can tell Notepad++ are not ported to Mac yet sadly.
SublimeText is an excellent editor - but does require a license (it can be used if you're willing to click through the occasional "buy me!" message). I found it to be worth the money to reward the developers.
There's also Microsoft's Visual Studio Code - basically a fancy programmer-oriented editor, but has many extensions to let you compile and debug in several languages (including C#).
I still love Notepad++ on Windows for heavy-lifting of text files, but for coding, Sublime and VSC are better (for me, at least!)
Microsoft have recently released Visual Studio for macOS in preview (it's basically a rebranded Xamarin developer studio with additional functionality and made to look more like Visual Studio on Windows) and it can be downloaded here: https://www.visualstudio.com/vs/visual-studio-mac/