C# Arrays versus List

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It is rare, in reality, that you would want to use an array. Definitely use a List<t> any time you want to add/remove data, since resizing arrays is expensive. If you know the data is fixed length, and you want to micro-optimise for some very specific reason (after benchmarking), then an array may be useful.

List<t> offers a lot more functionality than an array (although LINQ evens it up a bit), and is almost always the right choice. Except for params arguments, of course ;-p

As a counter - List<t> is one-dimensional; where-as you have have rectangular (etc) arrays like int[,] or string[,,] - but there are other ways of modelling such data (if you need) in an object model.

See also:

How/When to abandon the use of Arrays in c#.net?[^]
Arrays, What's the point?[^]
That said, I make a lot of use of arrays in my protobuf-net[^] project; entirely for performance:

it does a lot of bit-shifting, so a byte[] is pretty much essential for encoding
I use a local rolling byte[] buffer which I fill before sending down to the underlying stream (and v.v.); quicker than BufferedStream etc
it internally uses an array-based model of objects (Foo[] rather than List<foo>), since the size is fixed once built, and needs to be very fast
But this is definitely an exception; for general line-of-business processing, a List<t> wins every time.

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Yes, pretty much. List<t> is a generic class. It supports storing values of a specific type without boxing to and unboxing from object. ArrayList simply stores object references. As a generic collection, it implements the generic IEnumerable<t> interface and can be used easily in LINQ (without requiring any Cast or OfType call).

ArrayList belongs to the days that C# didn't have generics. It's deprecated in favor of List<t>. You shouldn't use ArrayList in new code that targets .NET >= 2.0 unless you have to interface with an old API that uses it.