Is all c# program code written in one Program.cs file?

Question

C++ / C#

In all tutorials, all program classes are written in one Program.cs file. Is it convenient? Or is it at the time of training so done to simplify?

Answer 1

This is done only during training or for very simple programs.

Answer 2

If you look at the structure of large projects, you can see that there is not only a division of classes into files, there are also folders that represent a namespace. In any project, writing everything in one file is insanity!