DictionaryDictionary is a collection of keys and values in C#. Dictionary is included in the System.Collection.Generics namespace.To declare a Dictionary −IDictionary d = new Dictionary();To add elements −IDictionary d = new Dictionary(); d.Add(1,97); d.Add(2,89); d.Add(3,77); d.Add(4,88);ArrayArray stores a fixed-size sequential collection of elements of the same type. It consists of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.To define Arrays −int[] arr = new int[5]; To initialize and set elements to Arrays.int[] arr = new int[10] {3, 5, 35, 87, 56, 99, 44, 36, 78};

finalJava has final keyword, but C# does not have its implementation. For the same implementation, use the sealed keyword.With sealed, you can prevent overriding of a method. When you use sealed modifiers in C# on a method, then the method loses its capabilities of overriding. The sealed method should be part of a derived class and the method must be an overridden method.FinallyThe finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.FinalizeThe ... Read More

ClassClass is a blueprint for a data type. A class definition starts with the keyword class followed by the class name.StructA structure is a value type data type. It helps you to make a single variable hold related data of various data types. The struct keyword is used for creating a structure.The following are the differences −Classes are reference types and structs are value typesStructures do not support inheritanceStructures cannot have default constructorWhen you create a struct object using the new operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the ... Read More

An array stores a fixed-size sequential collection of elements of the same type, whereas list is a generic collection.To define a List −List

To implement Remove() and RemoveAt() methods in C#, try the following code −Firstly, set a list.List myList = new List() {    "mammals",    "reptiles",    "amphibians",    "vertebrate" };Now, use Remove() method to remove an element.myList.Remove("reptiles");Now, use RemoveAt() method to remove an element by setting the position.myList.RemoveAt(2);The following is the complete code −Exampleusing System; using System.Collections.Generic; using System.Linq; class Program {    static void Main() {       List myList = new List() {          "mammals",          "reptiles",          "amphibians",          "vertebrate"       ... Read More

Declaring an array does not initialize the array in the memory. When the array variable is initialized, you can assign values to the array.Array is a reference type, so you need to use the new keyword to create an instance of the array. For example, assign the values like the following statement −double[] price = new double[5]; price[0] = 3245.50; price[1] = 1234.50; price[2] = 8765.50; price[3] = 5784.50; price[4] = 6576.50;We assigned five values above to the price array. You can assign values to the array at the time of declaration.double[] price = new double[5] {3245.50, 1234.50, 8765.50, 6576.50;};

Java has a final keyword, but C# does not have its implementation. Use the sealed or readonly keyword in C# for the same implementation.The readonly would allow the variables to be assigned a value only once. A field marked "read-only", can only be set once during the construction of an object. It cannot be changed.Exampleclass Employee {    readonly int age;    Employee(int age) {       this.age = age;    }    void ChangeAge() {          //age = 27; // Compile error    } }Above, we have set the age field as readonly, which once assigned cannot be changed.

HashSet in C# eliminates duplicate strings or elements in an array.In C#, it is an optimized set collection.Let us see an example to remove duplicate strings using C# HashSet −Exampleusing System; using System.Collections.Generic; using System.Linq; class Program {    static void Main() {       string[] arr1 = {          "one",          "two",          "two",          "one",          "three"       };       Console.WriteLine(string.Join(",", arr1));       // HashSet       var h = new HashSet(arr1);       // eliminates duplicate words       string[] arr2 = h.ToArray();       Console.WriteLine(string.Join(",", arr2));    } }To declare HashSet.var h = new HashSet

Firstly, set the original array −int[] arr = { 1, 2,3 }; // Original Array Console.WriteLine("Original Array= "); fo            reach (int i in arr) {    Console.WriteLine(i); }Now, use the Array.reverse() method to reverse the array −Array.Reverse(arr);The following is the complete code to reverse an array in C# −Exampleusing System; class Demo {    static void Main() {       int[] arr = { 9, 32, 87, 45, 77, 56 };       // Original Array       Console.WriteLine("Original Array= ");       foreach (int i in arr) {          Console.WriteLine(i);       }       // Reverse Array       Array.Reverse(arr);       Console.WriteLine("Reversed Array= ");       foreach (int j in arr) {          Console.WriteLine(j);       }       Console.ReadLine();    } }

Java has a final keyword, but C# does not have its implementation. For the same implementation, use the sealed keyword.With sealed, you can prevent overriding of a method. When you use sealed modifiers in C# on a method, then the method loses its capabilities of overriding. The sealed method should be part of a derived class and the method must be an overridden method.The following example won’t allow you to override the method display() because it has a sealed modifier for the ClassTwo derived class.ClassOne is our base class, whereas ClassTwo and ClassThree are derived classes −Exampleclass ClassOne {   ... Read More