46. What are collections in C#?
Groups of objects. Examples: Array, List, Dictionary, HashSet.
47. Difference between Array and List?
- Array: fixed size
- List: dynamic, part of System.Collections.Generic
48. Difference between List and LinkedList?
- List: array-based, fast indexing
- LinkedList: node-based, fast insertion/deletion
49. Difference between Dictionary and Hashtable?
- Dictionary<K,V>: Generic, type-safe
- Hashtable: Non-generic, stores objects
50. Difference between Stack and Queue?
- Stack: LIFO
- Queue: FIFO
51. What is ConcurrentDictionary?
Thread-safe dictionary for multi-threaded environments.
52. What is IEnumerable vs ICollection?
- IEnumerable: read-only, allows iteration
- ICollection: adds Count, Add, Remove methods
53. What is IList?
Provides index-based access to a collection.
54. What is ObservableCollection?
Collection that raises events when items are added/removed, useful for data binding.
55. What is a generic type?
Type parameterized classes/methods for type safety.
56. Example of a generic method:
public T Max<T>(T a, T b) where T : IComparable<T> => a.CompareTo(b) > 0 ? a : b;57. Difference between List<T> and IEnumerable<T>?
List<T> is a concrete collection; IEnumerable<T> is an interface for iteration.
58. What is ReadOnlyCollection?
Wraps a collection to prevent modification.
59. What is SortedList vs SortedDictionary?
- SortedList: array-based, slower insertion, fast access
- SortedDictionary: tree-based, faster insertion
60. Difference between HashSet and List?
HashSet prevents duplicates, optimized for lookups.