C# INDEXER and OVERRIDE INDEXER, C#

Language: Layout:

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

namespace Rextester
{
    public class clsIndexer
    {
     
        string[] str= new string[3];
        
        public string this[int index]
        {
            get
            {
                return str[index];
            }
            set
            {
                str[index] = value;
            }
        }
        
        //override indexer
        public string this[string strIndex]
        {
            get
            {
                foreach (string s in str)
                {
                    if(s.ToLower() == strIndex.ToLower()) 
                        return s.ToString().ToUpper();
                }
                return null;
            }
            
        }
            
    }
        
    public class Program
    {
        public static void Main(string[] args)
        {
            clsIndexer objIndexer = new clsIndexer();
            objIndexer[0] = "Sachin";
            objIndexer[1] = "Sampat";
            objIndexer[2] = "Mayur";
            
            for(int i = 0; i < 3 ; i++){
                //calling indexer propery created with int type
                Console.WriteLine(objIndexer[i]);
            }
            
            Console.WriteLine("\n");
            //calling overriden indexer propery created with string type
            Console.WriteLine(objIndexer["Sachin"]);
            Console.WriteLine(objIndexer["Sampat"]);
            Console.WriteLine(objIndexer["Mayur"]);
        }
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,16 sec, absolute running time: 0,09 sec, cpu time: 0,09 sec, average memory usage: 12 Mb, average nr of threads: 2