Can const variables not be changed?

An explanation of const occurs at https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/const. There's also a readonly modifier. Usually you lock down access and try and make things as predictable as possible. I assume both const and private fields are ultimately for really making things predictable, and making sure the value is what you think it is. There's some discussion I found useful at https://www.c-sharpcorner.com/UploadFile/0c1bb2/read-only-and-constant-in-C-Sharp/ . I think C# want you to be sure that a const is a constant by definition (eg. pi). Some compiled languages replace references to constants with values during the compile step and can create dangerous inconsistencies if the value changes and you don't recompile everything.