Unity - says you're using C# version 4 and how to fix it

I had this problem. I was programming a project in Unity 2018 and everything went along fine. Then I loaded an old project from an older version of Unity and imported it into Unity 2018. After adding code and trying to compile it Unity told me what I was doing was not valid in C# version 4.... What the fuzz? Who's using C# version 4! I'm certainly not this is Unity 2018!

I believe for me the problem was the fact I had imported a project with a older version of .net into Unity 2018. However the fix may work no matter why you are getting informed by Unity you're using an older version of C#.

FIX:
In the build settings > player settings >
Go to Configuration... see picture below... and change the version of .net your project is using

The red arrow is meant to be pointing at "Scripting Runtime Version" and "Api Compatibility Level" Those are the two settings that may need to be changed if you have the problem of Unity telling you your code won't work in C# version 4 and you need to upgrade.

 

Wow thanks for posting the solution, too!