The convention is not to call it something dot txt but something dot C, just a convention.

但这个文件并不是以XX，txt命名,而是以XX，c命名，这只是一种约定而已。

哈佛公开课 - 计算机科学课程节选

I'm gonna call my file hello.c. There's a little bit GUI-- of distraction here but this is because this is not a GUI, CLI a graphical user interface, this is a CLI, command-line interface, which just means there are no windows and icons.

我先给我的文件命名为“hello，c“,你们也许会觉得有点烦，因为不是，图形用户界面，这是，命令行界面，这意味着没有窗口，没有图标。

哈佛公开课 - 计算机科学课程节选