The indexer is a class property that’s treated an object as an array. Or in other word indexer is a class property that’s access a class or structure in the same way as arrays.When you define an indexer for a class, then this class behaves similar to virtual array. You also access the instance of an object of this class using array access operator []. The indexer is also similar to a property. You use get and set accessors for defining an indexer. Indexer defines with ‘this’ keyword. It's not defined with names.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Collections;
 
namespace Learn
{
    public class Program
    {
        public static void Main()
        {
            StringDataStore stringStore = new StringDataStore();
            stringStore [0] = "First";
            stringStore [1] = "Second";
            stringStore [2] = "Third";
            stringStore [3] = "Fourth";
            for (int i = 0; i < 10; i++)
                Console.WriteLine(stringStore [i]);
            Console.ReadLine();
        }
    }
 
    public class StringDataStore
    {
        private string[] stringArr = new string[10]; // internal data storage
        public StringDataStore()
        {
 
        }
 
        public string this[int indx]
        {
            get
            {
                if (indx < 0 && indx >= stringArr.Length)
                    throw new IndexOutOfRangeException("Cannot store more than 20 bjects");
 
                return stringArr [indx];
            }
            
            set
            {
                if (indx < 0 && indx >= stringArr.Length)
                    throw new IndexOutOfRangeException("Cannot store more than 20 bjects");
 
                stringArr [indx] = value;
            }
        }
    }
}

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