C# provides several collection classes for storing and accessing multiple objects. The main collection classes include generic List, Dictionary, SortedList, Stack, Queue as well as non-generic ArrayList, Hashtable. Collections allow objects to be dynamically added and removed, unlike arrays which have a fixed size. Common collection operations include adding, removing, and accessing objects.

2. What is collection in c sharp
 C# collections perform all the data structure work. Just like an array, a collection
can also be used to store objects with an advantage over an array.
 In a collection, the stored object can grow or shrink dynamically, however, in an
array, there is a size limit.

3. Types of Collections:
 To work with the collections in C#, one can use any of the three namespaces that are listed below:
• System.Collections.Generic classes
• System.Collections classes (Now deprecated)
• System.Collections.Concurrent classes

4. Generic Collections
 The classes of the System.Collections.Generic namespace are listed below:
• List<T>
• Stack<T>
• Queue<T>
• Dictionary<Tkey,Tvalue>
• SortedList<Tkey,Tvalue>

5. List<T>
 Generic List<T> contains elements of specified type. It grows automatically as you add elements in it.
 The List<T> is a collection of strongly typed objects that can be accessed by index and having methods
for sorting, searching, and modifying list.
 It is the generic version of the ArrayList that comes under System.Collections.Generic namespace.
 To create a List,
List<int> primeNumbers = new List<int>();
primeNumbers.Add(1); // adding elements using add() method
primeNumbers.Add(3);
primeNumbers.Add(5);
primeNumbers.Add(7);

6. Method Usage
Add Adds an element at the end of a List<T>.
AddRange Adds elements of the specified collection at the end of a List<T>.
BinarySearch Search the element and returns an index of the element.
Clear Removes all the elements from a List<T>.
Contains Checks whether the specified element exists or not in a List<T>.
Foreach Iterates through a List<T>.
Insert Inserts an element at the specified index in a List<T>.
InsertRange Inserts elements of another collection at the specified index.
Remove Removes the first occurrence of the specified element.
RemoveAt Removes the element at the specified index.
Sort Sorts all the elements.

7. Dictionary<Tkey,Tvalue>
 The Dictionary<TKey, TValue> is a generic collection that stores key-value pairs in no particular order and comes
under System.Collections.Generic namespace.
 Implements IDictionary<TKey, TValue> interface.
 Keys must be unique and cannot be null.Values can be null or duplicate.
 Values can be accessed by passing associated key in the indexer e.g. myDictionary[key]
 Elements are stored as KeyValuePair<TKey, TValue> objects.
 To create a Dictionary,
IDictionary<int, string> numberNames = new Dictionary<int, string>();
numberNames.Add(1,"One"); //adding a key/value using the Add() method
numberNames.Add(2,"Two");
numberNames.Add(3,"Three");

8. Method Usage
Add(Tkey,TValue) Adds the specified key and value to the dictionary.
Clear() Removes all keys and values from the Dictionary<TKey,TValue>.
ContainsKey(Tkey) Determines whether the Dictionary<TKey,TValue> contains the
specified key.
ContainsValue(Tvalue) Determines whether the Dictionary<TKey,TValue> contains a
specific value.
Remove(Tkey) Removes the value with the specified key from the
Dictionary<TKey,TValue>.

9. SortedList<Tkey,Tvalue>
 SortedList stores key and value pairs. It automatically adds the elements in ascending order of a key by default.
 A key must be unique and cannot be null. A value can be null or duplicate.
 It is faster in the retrieval of data once sorted, whereas SortedDictionary<TKey, TValue> is faster in insertion and
removing key-value pairs.
 To create a SortedList,
SortedList<int, string> numberNames = new SortedList<int, string>();
numberNames.Add(3, "Three");
numberNames.Add(1, "One");
numberNames.Add(2, "Two");

10. Methods Usage
Add(Tkey,Tvalue) Adds an element with the specified key and value into the
SortedList<TKey,TValue>
Clear() Removes all keys and values from the SortedList<TKey,TValue >.
ContainsKey(Tkey) Determines whether the SortedList<TKey,TValue > contains the
specified key.
ContainsValue(Tvalue) Determines whether the SortedList<TKey,TValue > contains a
specific value.
Remove(Tkey) Removes the value with the specified key from the
SortedList<TKey,TValue >.

11. Queue<T>
 Queue is a special type of collection that stores the elements in FIFO style (First In First Out).
 It contains the elements in the order they were added.
 Elements can be added using the Enqueue() method. Cannot use collection-initializer syntax.
 Elements can be retrieved using the Dequeue() and the Peek() methods. It does not support an
indexer.

12.  To create a Queue,
Queue<int> callerIds = new Queue<int>();
callerIds.Enqueue(1);
callerIds.Enqueue(2);
callerIds.Enqueue(3);
callerIds.Enqueue(4);
Methods Usage
Enqueue(T) Adds an item into the queue.
Dequeue Returns an item from the beginning of the queue and removes it from
the queue.
Peek() Returns an first item from the queue without removing it.
Contains(T) Checks whether an item is in the queue or not
Clear() Removes all the items from the queue.

13. Stack<T>
 Stack is a special type of collection that stores elements in LIFO style (Last In First Out).
 Elements can be added using the Push() method. Cannot use collection-initializer syntax.
 Elements can be retrieved using the Pop() and the Peek() methods. It does not support an indexer.
 To create Stack,
Stack<int> myStack = new Stack<int>();
myStack.Push(1);
myStack.Push(2);
myStack.Push(3);
myStack.Push(4);

14. Method Usage
Push(T) Inserts an item at the top of the stack.
Peek() Returns the top item from the stack.
Pop() Removes and returns items from the top of the stack.
Contains(T) Checks whether an item exists in the stack or not.
Clear() Removes all items from the stack.

15. Non-generic Collections
 The classes of the System.Collections namespace are listed below:
• ArrayList
• Stack
• Queue
• SortedList
• Hashtable

16. ArrayList
 The ArrayList is a non-generic collection of objects whose size increases dynamically.
 The ArrayList class included in the System.Collections namespace. Create an object of the ArrayList
using the new keyword.
var arlist1 = new ArrayList();
arlist1.Add(1);
arlist1.Add("Bill");
arlist1.Add(" ");

17. Method Usage
Add() Add() method adds single elements at the end of ArrayList.
AddRange() adds all the elements from the specified collection into ArrayList.
Insert() to insert a single elements at the specified index in ArrayList.
InsertRange() insert all the elements of the specified collection starting from
specified index in ArrayList.
Remove() removes the specified element from the ArrayList.
Contains() Checks whether specified element exists in the ArrayList or not.
Returns true if exists otherwise false.
Sort() Sorts entire elements of the ArrayList.

18. Stack
 Stack stores the values in LIFO style (Last In First Out).
 It provides a Push() method to add a value and Pop() & Peek() methods to retrieve values.
 C# includes both, generic and non-generic Stack.

19. Queue
 Queue stores the values in FIFO style (First In First Out).
 It keeps the order in which the values were added.
 It provides an Enqueue() method to add values and a Dequeue() method to retrieve values from
the collection.
 C# includes generic and non-generic Queue.

20. Hashtable
 The Hashtable is a non-generic collection that stores key-value pairs, similar to generic
Dictionary<TKey, TValue> collection.
 Keys must be unique and cannot be null.Values can be null or duplicate.
 Values can be accessed by passing associated key in the indexer e.g. myHashtable[key]
 To create Hashtable,
Hashtable numberNames = new Hashtable();
numberNames.Add(1,"One"); //adding a key/value using the Add() method
numberNames.Add(2,"Two");
numberNames.Add(3,"Three");

21. System.Collections.Concurrent classes:
 The classes for thread-safe operations are facilitated by the System. Now multiple threads will not
create problem for accessing the collection items.
• BlockingCollection
• ConcurrentBag
• ConcurrentStack
• ConcurrentQueue
• ConcurrentDictionary

22. QUESTIONS?

23. THANKS,