C# ArrayList

In C#, an ArrayList stores elements of multiple data types whose size can be changed dynamically. For example,

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList
        ArrayList student = new ArrayList();

        // add elements to ArrayList
        student.Add("Jackson");
        student.Add(5);

        // display every element of myList 
        for (int i = 0; i < student.Count; i++)
        {
            Console.WriteLine(student[i]);
        }
    }
}

Output

Jackson
5

Here, student is an ArrayList that contains elements ("Jackson" and 5) of different data types.

We will learn about ArrayList in detail.

Create an ArrayList

To create ArrayList in C#, we need to use the System.Collections namespace. Here is how we can create an arraylist in C#.

// create an arraylist
ArrayList myList = new ArrayList();

Here, we have created an arraylist named myList.

Basic Operations on ArrayList

In C#, we can perform different operations on arraylists. We will look at some commonly used arraylist operations in this tutorial:

• Add Elements
• Access Elements
• Change Elements
• Remove Elements

Let's see how we can perform these operations in detail!

Add Elements in ArrayList

C# provides a method Add() using which we can add elements in ArrayList. For example,

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList
        ArrayList student = new ArrayList();

        // add elements to ArrayList
        student.Add("Tina");
        student.Add(5);

    }
}

In the above example, we have created an ArrayList named student.

Then we added "Tina" and 5 to the ArrayList using the Add() method.

Note: ArrayList stores elements with different data types. However, if you want to store elements of the same data type use List<T> class instead.

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList using var  
        ArrayList myList = new ArrayList() { "Pizza", 24, "Pen" };

        // iterate through items
        for (int i = 0; i < myList.Count; i++)
        {
            Console.WriteLine(myList[i]);
        }
    }
}

Pizza
24
Pen

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList 
        ArrayList myList = new ArrayList();

        myList.Add("Jimmy");
        myList.Add("Blake");
        myList.Add("Taylor");

        Console.WriteLine("Before Inserting: " + myList[1]);

        // insert "Tim" at first index position 
        myList.Insert(1, "Tim");

        Console.WriteLine("After Inserting: " + myList[1]);
    }
}

Before Inserting: Blake
After Inserting: Tim

Access ArrayList Elements

We use indexes to access elements in ArrayList. The indexing starts from 0. For example,

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList 
        ArrayList schoolDetails = new ArrayList();
        schoolDetails.Add("Mary's");
        schoolDetails.Add("France");
        schoolDetails.Add(23);

        // access the first element 
        Console.WriteLine("First element: " + schoolDetails[0]);

        // access the second element 
        Console.WriteLine("Second element: " + schoolDetails[1]);
    }
}

Output

First element: Mary's
Second element: France

Since the index of the ArrayList starts from 0:

• schoolDetails[0] - accesses the first element
• schoolDetails[1] - accesses the second element

Iterate ArrayList

In C#, we can also loop through each element of ArrayList using a for loop. For example,

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList containing 3 elements 
        ArrayList myList = new ArrayList();

        myList.Add("Science");
        myList.Add(true);
        myList.Add(5);

        // display every element of myList 
        for (int i = 0; i < myList.Count; i++)
        {
            Console.WriteLine(myList[i]);
        }
    }
}

Output

Science
True
5

In the above example, we have looped through myList using a for loop.

Here, myList.Count gives the number of elements in myList.

Change ArrayList Elements

We can change the value of elements in ArrayList as:

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList 
        ArrayList myList = new ArrayList();

        myList.Add("Harry");
        myList.Add("Miller");

        Console.WriteLine("Original Second element: " + myList[1]);

        // change the value of second element 
        myList[1] = "Styles";
        Console.WriteLine("Updated second element: " + myList[1]);
    }
}

Output

Original Second element: Miller
Updated second element: Styles

Here, we have changed the value of the second element in myList.

Remove ArrayList Elements

C# provides methods like Remove(), RemoveAt(), RemoveRange() to remove elements from ArrayList.

We will see an example below using Remove() to a remove element:

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList 
        ArrayList myList = new ArrayList();
        myList.Add("Jack");
        myList.Add(4);
        myList.Add("Jimmy");

        // remove "Jack" from myList
        myList.Remove("Jack");

        // iterate through myList after removing "Jack"
        for (int i = 0; i < myList.Count; i++)
        {
            Console.WriteLine(myList[i]);
        }
    }
}

Output

4
Jimmy

In the above example, we have removed "Jack" from myList using the Remove() method.

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList using var  
        var person = new ArrayList();
        person.Add("Chris");
        person.Add(45);

        Console.WriteLine("Element at first index: " + person[1]);

    }
}

Element at first index: 45

using System;
using System.Collections;

class Program
{
    public static void Main()
    {
        // create an ArrayList 
        var myList = new ArrayList() { "Delicate", "Willow", "Style", 3 };

        // check whether myList contains "Willow"  
        var result = myList.Contains("Willow");
        Console.WriteLine(result);
    }
}

True