How to use C# ArrayList Class

The ArrayList class is designed to hold heterogeneous collections of objects. However, it doesn't always offer the best performance. I think you should use List<T> instead of using ArrayList

To play demo you need to create a new console project, then add code as below

using System;
using System.Collections;

namespace ConsoleApp
{
    class Program
    {
        static void Main(string[] args)
        {
            //Init ArrayList
            ArrayList list = new ArrayList();
            list.Add("One");
            list.Add(2);
            list.Add("Three");
            list.Add(4);
            //Get item in ArrayList using for loop
            for (int i = 0; i < list.Count; i++)
                Console.WriteLine("{0}", list[i]);
            //Get item in ArrayList using foreach loop
            foreach (var i in list)
                Console.WriteLine($"{i}");            
            Console.ReadLine();
        }
    }
}

You can see the ArrayList is one of the most flexible data structure from C# collections. You can Sort, Join, Remove, Find...items from ArrayList

// Remove element in ArrayList at position 1
list.RemoveAt(1);
// Insert word at the beginning of ArrayList.
list.Insert(0, "C#");
// Remove first two words from ArrayList.
list.RemoveRange(0, 2);
// Sort the ArrayList.
list.Sort();
// Clear all items in ArrayList.
list.Clear();
// Count items in ArrayList
Console.WriteLine(list.Count);
//Init ArrayList
ArrayList list2 = new ArrayList();
list2.Add("c-sharpcode.com");
list.AddRange(list2);