C#

List is a generic collection class and can used for storing items of different data types.For using Using Generic List (List<T>)in C# we need to import System.Collections.Generic namespace. List<T> is defined in this namespace.

Creating list class object

To use List<T> object we need to declare and create an object of List type.In the following example we are creating an object of list class of Student type.

List<Student> students = new List<Student>();

Adding elements to list

We can add elements to the student list using the Add method of the list class:

students.Add(new Student { Name = "Amit", Class = 12 });
students.Add(new Student{Name="John",Class=10});
students.Add(new Student{Name="Raj",Class=8});
students.Add( new Student{Name="Greg",Class=12});
students.Add( new Student{Name="Priya",Class=12})

Instead of declaring list object and adding elements in separate lines we can add elements to the list when creating object of List.

var students=new List<Student>{
new Student{Name="Amit",Class=12},
new Student{Name="John",Class=10},
new Student{Name="Raj",Class=8},
new Student{Name="Greg",Class=12},
new Student{Name="Priya",Class=12},
};

We can create List<T> of any type.We can create a List of string type as:

List<string> names = new List<string>();

Iterating list elements using Foreach loop

We can iterate the elements of the list as:

foreach(var student in students)
{
Console.WriteLine(student);
}

An important point to remember is that we can not modify the list elements using the foreach loop.We can just read the value of list elements using foreach loop.

Following are some of the useful methods of the List class:

• Insert(index,item)    inserts an item at a specific position in the List
• Remove (item)  removes the specified item from the list
• Sort() sorts the items in the list
• Contains(item)  checks if an item exists in the list
• ToArray()  converts the List to an array

List example

In the following example we are adding elements to the list then using the list methods we are performing different actions:

List<string> names = new List<string>();
names.Add("Amit");
names.Insert(0,"John");//John is the first element in the list
names.Sort();//Now Amit is the first element in the list

if(names.Contains("Amit"))
{
Console.WriteLine("name found");
}

Type Safety

One of the advantages that List<T> have is that it provides compile time type checking.For example if we declare a List<string> of string type then we can not add int elements in that List.This prevent run time error which would occur if we don’t use generic list and rather use ordinary arraylist.

Follow on:

To extract substring C# provides substring method.But unlike VB.NET in C# there is no left and right methods to extract left and right substrings.
If we need to extract left and right substrings then we need to write custom logic to extract left and right side substrings.

Left and Right substring methods in C#

Following class is an extension class which declares the methods called ExtractLeft and ExtractRight to extract left and right substrings from the main string.

public static class StringExt
{
public static string ExtractLeft(this string originalString, int nofChars)
{
//retrun left string
string leftString = originalString.Substring(0, nofChars);
return leftString;
}
public static string ExtractRight(this string originalString, int nofChars)
{
//retrun right string abcdefg
string result = originalString.Substring(originalString.Length - nofChars, nofChars);
return result;
}
}

We are calling the above methods in the following example:

string leftStr = "This is a sample string";
string leftchars=leftStr.ExtractLeft(2);
string rightchars = leftStr.ExtractRight(5);

we get the following return values in the above example

ng
tring

Follow on:

Array is a useful data type used for storing multiple values.Arrays in c# like other languages are used for storing multiple variables of the same type.So instead of using multiple variables for storing values
we can use arrays.

Array declaration

We can declare and create array in a single line as:

int[] nos=new int[10];

or we can declare and then create array separately:

int[] nos;
nos=new int[10];

Since arrays are implemented as objects in c# ,so array object is actually created only when we instantiate an array using new operator.

To initialize array we can assign the values when declaring array.We don’t need to assign array size when declaring and assigning array in the same line.

int[] nos = { 1, 2, 3, 4, 5, 6 };

We can iterate array elements using for loop as in other languages:

for (int i = 0; i < nos.Length;i++ )
{
Console.WriteLine(nos[i]);
}

Since array index starts from 0 and continues till size of array minus 1 ,we start from 0 index when using for loop.

But a better way to iterate array elements is to use foreach loop:

foreach(int no in nos)
{
Console.WriteLine(no);
}

An important feature of arrays in c# is that array implements IEnumerable interface so we can use the methods of IEnumerable interface such as foreach loop.

Every array in C# is an object derived from the System.Array class.So the members of System.Array class can be used by every array.

Following are some of the useful methods defined by the array class

• Sort         sorts the array elements
• ToString      returns string
• Resize<T>        modifies the size of the array
• Reverse           reverses the elements of the array
• GetLength      returns length of the array
• Find<T>         used to search for an element in array as defined by the predicate passed as argument
• Exists<T>      used to search for existence of an element in array as defined by the predicate passed as argument

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