Array vs List in C#: which should I use?

Short answer

Use List<T> by default — it grows, and it has the methods you want. Use an array when the size is genuinely fixed and known, or when an API demands one.

csharp

int[] fixedScores = new int[3];           // fixed length, forever
int[] literal = { 88, 92, 79 };

var scores = new List<int> { 88, 92, 79 };
scores.Add(95);
scores.Remove(79);

#What List gives you

csharp

scores.Add(x);  scores.AddRange(other);
scores.Insert(0, x);
scores.Remove(x);  scores.RemoveAt(0);
scores.Contains(x);  scores.IndexOf(x);
scores.Sort();  scores.Reverse();
scores.Count;

Note Count on a List and Length on an array — a small inconsistency that trips people up constantly.

#How List grows

Internally it is an array. When it fills up, it allocates a new one at double the capacity and copies. If you know roughly how many items you will add, pre-size it:

csharp

var scores = new List<int>(1000);

#Other collections worth knowing

Need	Type
Key to value	`Dictionary<K,V>`
Unique items, fast lookup	`HashSet<T>`
First in, first out	`Queue<T>`
Last in, first out	`Stack<T>`
Read-only view	`IReadOnlyList<T>`
Thread-safe	`ConcurrentDictionary<K,V>`

#Accept the interface, return the concrete type

csharp

void Process(IEnumerable<int> items) { }     // accepts arrays, lists, LINQ results
List<int> Build() => new();

Accepting IEnumerable<T> makes your method usable with any sequence.

#What List gives you

#How List grows

#Other collections worth knowing

#Accept the interface, return the concrete type

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