Question

When creating DLL files for a program that already exists, is it customary to create them by going to

File >
New >
Project >
Class Library,

File >
Add >
New Project >
Class Library,

or

File >
Add >
Existing Project >
Class Library?

Answer 1

You should differentiate 2 things:

1. DLLs – compiled code in machine (in case of .net, clr) readable format for execution
2. Code – source code files that get compiled into DLLs.

If you have a dll that you can use, you add it as a reference to your project.
If you have source codes, you can add them the way you specified (add existing project). If you want to write new .dll, you should use “Create new class library”. Note that whenever you add through “Add existing project”, project (along with source codes) isn’t copied to your solution folder.

Basics you should know before you go on:

1. Solution – means to tie several projects together into one logical bunch.
2. Project – means to tie several source code files/resources/etc. into one logical bunch that gets compiled into one physical unit – dll/exe/etc.
3. Source file – code file like MyClass.cs. This is where the code is written.
4. Reference – reference from one project to another one in order to obtain/use public-visible functionality.

I’d recommend reading some books on C#/.NET to get clearer understanding.