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Interview question and answer on C# Collection framework

VINNER TECH June 19, 2023

Interview question and answer on C# Collection framework with full explanation and code example.




Here are the top 25 interview questions and answers on C# Collection framework, along with detailed explanations and code examples:

  1. Q: What is a collection in C#? A: A collection in C# is a group of related objects that can be accessed and manipulated as a single unit. It provides various data structures and algorithms to store and manage data efficiently.

  2. Q: What are the main types of collections in C#? A: The main types of collections in C# are:

    • Lists: Ordered collection of elements.
    • Arrays: Fixed-size collection of elements.
    • Dictionaries: Key-value pairs collection.
    • Queues: First-in, first-out (FIFO) collection.
    • Stacks: Last-in, first-out (LIFO) collection.
    • Sets: Unique collection of elements.

  3. Q: Explain the List collection in C#. A: List is an ordered collection that allows duplicate elements. It provides dynamic resizing, indexing, searching, sorting, and other operations. Here's an example:

    csharp
    List<int> numbers = new List<int>();
numbers.Add(1);
numbers.Add(2);
numbers.Add(3);
Console.WriteLine(numbers[1]);  // Output: 2

  4. Q: What is the difference between an array and a List? A: Arrays have a fixed size, while Lists can dynamically resize. Arrays use square brackets for indexing, while Lists use the Indexer property. Arrays require manual resizing, while Lists handle resizing automatically.

  5. Q: Explain the Dictionary collection in C#. A: Dictionary is a collection of key-value pairs. It provides fast lookup and retrieval of elements based on the key. Duplicate keys are not allowed. Here's an example:

    csharp
    Dictionary<string, int> ages = new Dictionary<string, int>();
ages.Add("John", 25);
ages.Add("Alice", 30);
Console.WriteLine(ages["John"]);  // Output: 25

  6. Q: What is the difference between a Dictionary and a Hashtable? A: Both Dictionary and Hashtable store key-value pairs, but Hashtable is a legacy class from earlier versions of .NET, while Dictionary is a generic class introduced in .NET 2.0. Dictionary provides type safety and better performance compared to Hashtable.

  7. Q: Explain the Queue collection in C#. A: Queue is a collection that follows the FIFO (First-In, First-Out) principle. It allows adding elements at the end and removing elements from the front. Here's an example:

    csharp
    Queue<string> names = new Queue<string>();
names.Enqueue("John");
names.Enqueue("Alice");
Console.WriteLine(names.Dequeue());  // Output: John

  8. Q: Explain the Stack collection in C#. A: Stack is a collection that follows the LIFO (Last-In, First-Out) principle. It allows adding elements at the top and removing elements from the top. Here's an example:

    csharp
    Stack<string> names = new Stack<string>();
names.Push("John");
names.Push("Alice");
Console.WriteLine(names.Pop());  // Output: Alice

  9. Q: Explain the HashSet collection in C#. A: HashSet is a collection that stores unique elements. It provides fast lookup and ensures that no duplicate elements are present. Here's an example:

    csharp
    HashSet<int> numbers = new HashSet<int>();
numbers.Add(1);
numbers.Add(2);
numbers.Add(2);  // Ignored (already exists)
Console.WriteLine(numbers.Count);  // Output: 2

  10. Q: What is the difference between a List and a HashSet? A: Lists allow duplicate elements, while HashSets store unique elements only. Lists maintain the insertion order, while HashSets do not guarantee any specific order.

  11. Q: Explain the SortedList collection in C#. A: SortedList is a collection that maintains the elements in sorted order based on the keys. It provides efficient searching, insertion, and removal of elements. Here's an example:

    csharp
    SortedList<int, string> items = new SortedList<int, string>();
items.Add(3, "Item 3");
items.Add(1, "Item 1");
items.Add(2, "Item 2");
Console.WriteLine(items.Values[1]);  // Output: Item 2

  12. Q: Explain the LinkedList collection in C#. A: LinkedList is a collection that represents a doubly-linked list. It allows efficient insertion, removal, and traversal of elements. Here's an example:

    csharp
    LinkedList<string> names = new LinkedList<string>();
names.AddLast("John");
names.AddLast("Alice");
Console.WriteLine(names.First.Value);  // Output: John

  13. Q: Explain the ObservableCollection collection in C#. A: ObservableCollection is a collection that provides notifications when the collection is modified. It is useful for data binding scenarios where UI elements need to be updated automatically. Here's an example:

    csharp
    ObservableCollection<string> names = new ObservableCollection<string>();
names.CollectionChanged += (sender, e) =>
{
    Console.WriteLine("Collection modified!");
};
names.Add("John");
  14. Q: Explain the BitArray collection in C#. A: BitArray is a collection that stores a compact array of Boolean values. It provides space-efficient storage and bitwise operations on the elements. Here's an example:
  15. csharp
    BitArray bits = new BitArray(4);
bits.Set(1, true);
bits.Set(3, true);
Console.WriteLine(bits.Get(3));  // Output: True

  16. Q: How do you iterate over elements in a collection? A: You can use loops such as foreach or for to iterate over elements in a collection. Here's an example with a List:

    csharp
    List<int> numbers = new List<int> { 1, 2, 3 };
foreach (int number in numbers)
{
    Console.WriteLine(number);
}

  17. Q: How do you check if a collection contains a specific element? A: You can use the Contains method to check if a collection contains a specific element. Here's an example:

    csharp
    List<string> names = new List<string> { "John", "Alice" };
bool containsJohn = names.Contains("John");
Console.WriteLine(containsJohn);  // Output: True

  18. Q: How do you sort elements in a collection? A: You can use the Sort method or the OrderBy LINQ extension method to sort elements in a collection. Here's an example with a List:

    csharp
    List<int> numbers = new List<int> { 3, 1, 2 };
numbers.Sort();
Console.WriteLine(string.Join(", ", numbers));  // Output: 1, 2, 3

  19. Q: How do you find the maximum or minimum element in a collection? A: You can use the Max or Min methods to find the maximum or minimum element in a collection. Here's an example:

    csharp
    List<int> numbers = new List<int> { 3, 1, 2 };
int maxNumber = numbers.Max();
int minNumber = numbers.Min();
Console.WriteLine(maxNumber);  // Output: 3
Console.WriteLine(minNumber);  // Output: 1

  20. Q: How do you remove elements from a collection? A: You can use methods like Remove, RemoveAt, or RemoveRange to remove elements from a collection. Here's an example with a List:

    csharp
    List<string> names = new List<string> { "John", "Alice", "Bob" };
names.Remove("Alice");
Console.WriteLine(string.Join(", ", names));  // Output: John, Bob

  21. Q: How do you clear all elements from a collection? A: You can use the Clear method to remove all elements from a collection. Here's an example:

    csharp
    List<int> numbers = new List<int> { 1, 2, 3 };
numbers.Clear();
Console.WriteLine(numbers.Count);  // Output: 0

  22. Q: How do you convert a collection to an array? A: You can use the ToArray method to convert a collection to an array. Here's an example:

    csharp
    List<int> numbers = new List<int> { 1, 2, 3 };
int[] array = numbers.ToArray();
Console.WriteLine(string.Join(", ", array));  // Output: 1, 2, 3

  23. Q: How do you convert a collection to a string? A: You can use the string.Join method to concatenate the elements of a collection into a single string. Here's an example:

    csharp
    List<string> names = new List<string> { "John", "Alice" };
string namesString = string.Join(", ", names);
Console.WriteLine(namesString);  // Output: John, Alice

  24. Q: How do you check if a collection is empty? A: You can use the Count property or the Any method to check if a collection is empty. Here's an example:

    csharp
    List<int> numbers = new List<int>();
bool isEmpty = numbers.Count == 0;
Console.WriteLine(isEmpty);  // Output: True

  25. Q: How do you copy elements from one collection to another? A: You can use methods like AddRange or Concat to copy elements from one collection to another. Here's an example:

    csharp
    List<int> numbers1 = new List<int> { 1, 2, 3 };
List<int> numbers2 = new List<int>();
numbers2.AddRange(numbers1);
Console.WriteLine(string.Join(", ", numbers2));  // Output: 1, 2, 3

  26. Q: How do you check if two collections are equal? A: You can use the SequenceEqual method to check if two collections have the same elements in the same order. Here's an example:

    csharp
    List<int> numbers1 = new List<int> { 1, 2, 3 };
List<int> numbers2 = new List<int> { 1, 2, 3 };
bool areEqual = numbers1.SequenceEqual(numbers2);
Console.WriteLine(areEqual);  // Output: True

These are some of the top interview questions and answers related to the C# Collection framework. Remember to understand the concepts and practice implementing them to gain confidence in using collections effectively in your code.

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