Concept of Namespaces in C#

Prepared By : Uday Shah - HOD (IT)
Contact No : 7600044051

Namespaces are heavily used in C# programming in two ways. First, the .NET Framework uses namespaces to organize its many classes, as follows

System.Console.WriteLine("Hello World!");

System is a namespace and Console is a class in that namespace. The using keyword can be used so that the complete name is not required, as in the following example

using System;
Console.WriteLine("Hello");
Console.WriteLine("World!");

Second, declaring your own namespaces can help you control the scope of class and method names in larger programming projects. Use the namespace keyword to declare a namespace, as in the following example:


namespace SampleNamespace
{
    class SampleClass
    {
        public void SampleMethod()
        {
            System.Console.WriteLine(
              "SampleMethod inside SampleNamespace");
        }
    }
}


Namespaces have the following properties:


They organize large code projects.


They are delimited by using the . operator.


The using directive obviates the requirement to specify the name of the namespace for every class.


The global namespace is the "root" namespace: global::System will always refer to the .NET Framework namespace System.

Concept of Delegates in C#

Prepared By : Uday Shah - HOD(IT)
Contact No : 7600044051

A delegate is a type that defines a method signature. When you instantiate a delegate, you can associate its instance with any method with a compatible signature. You can invoke (or call) the method through the delegate instance.

Delegates are used to pass methods as arguments to other methods. Event handlers are nothing more than methods that are invoked through delegates. You create a custom method, and a class such as a windows control can call your method when a certain event occurs. The following example shows a delegate declaration

public delegate int PerformCalculation(int a, int b);

Any method from any accessible class or struct that matches the delegate's signature, which consists of the return type and parameters, can be assigned to the delegate. The method can be either static or an instance method. This makes it possible to programmatically change method calls, and also plug new code into existing classes. As long as you know the signature of the delegate, you can assign your own method.

Concept of Indexers in C#

Prepared By : Uday Shah - HOD (IT)
Contact No : 7600044051

Indexers allow instances of a class or struct to be indexed just like arrays. Indexers resemble properties except that their accessors take parameters.

In the following example, a generic class is defined and provided with simple get and set accessor methods as a means of assigning and retrieving values. The Program class creates an instance of this class for storing strings.

class SampleCollection<T>
{
    // Declare an array to store the data elements. 
    private T[] arr = new T[100];

    // Define the indexer, which will allow client code 
    // to use [] notation on the class instance itself. 
    // (See line 2 of code in Main below.)         
    public T this[int i]
    {
        get
        {
            // This indexer is very simple, and just returns or sets 
            // the corresponding element from the internal array. 
            return arr[i];
        }
        set
        {
            arr[i] = value;
        }
    }
}

// This class shows how client code uses the indexer. 
class Program
{
    static void Main(string[] args)
    {
        // Declare an instance of the SampleCollection type.
        SampleCollection<string> stringCollection = new SampleCollection<string>();

        // Use [] notation on the type.
        stringCollection[0] = "Hello, World";
        System.Console.WriteLine(stringCollection[0]);
    }
}
// Output: 
// Hello, World.

Using foreach with Arrays in C#

int[] numbers = { 4, 5, 6, 1, 2, 3, -2, -1, 0 };
foreach (int i in numbers)
{
    System.Console.Write("{0} ", i);
}
// Output: 4 5 6 1 2 3 -2 -1 0

The following examples create single-dimensional, multidimensional, and jagged arrays in C#

class TestArraysClass
{
    static void Main()
    {
        // Declare a single-dimensional array  
        int[] array1 = new int[5];

        // Declare and set array element values 
        int[] array2 = new int[] { 1, 3, 5, 7, 9 };

        // Alternative syntax 
        int[] array3 = { 1, 2, 3, 4, 5, 6 };

        // Declare a two dimensional array 
        int[,] multiDimensionalArray1 = new int[2, 3];

        // Declare and set array element values 
        int[,] multiDimensionalArray2 = { { 1, 2, 3 }, { 4, 5, 6 } };

        // Declare a jagged array 
        int[][] jaggedArray = new int[6][];

        // Set the values of the first array in the jagged array structure
        jaggedArray[0] = new int[4] { 1, 2, 3, 4 };
    }
}