Code compatibility between Unity 4.3 and UNity 2018.2

I know that there are a lot of differences between UNity 4.3 and Unity 2018.2. But will C# code written in Unity 4.3 still work in UNity 2018.2 with modification? Will Unity do this automatically on loading? The reason for asking this is if it is a positive answer I will do the Udemy course directly with Unity 2018.2 which I already have without downloading a very old, almost redundant version of Unity.

Most of the code should all be the same. Throughout the versions there are some commands and properties that have been deprecated, and unity isnt going to automatically fix those, but it should be relatively easy. Just go for it, if you run into an error, research. I would just follow the courses using 2018 and do your best with the few changes.