The Hashtable class represents a collection of key-and-value pairs that are organized based on the hash code of the key. It uses the key to access the elements in the collection.

A hash table is used when you need to access elements by using key, and you can identify a useful key value. Each item in the hash table has a key/value pair. The key is used to access the items in the collection.

using System;
using System.Collections;
namespace CollectionsApplication
{
    class Program
    {
        static void Main(string[] args)
        {
            Hashtable ht = new Hashtable();
            ht.Add("001", "Aditya Kumar");
            ht.Add("002", "Manoj Singh");
            ht.Add("003", "Sohel safe");
            ht.Add("004", "V.k Patel");
            ht.Add("005", "Atul Varma");
            ht.Add("006", "M. Arif");
            ht.Add("007", "Ritesh Saikia");
            if (ht.ContainsValue("Visal Pateker"))
            {
                Console.WriteLine("This employee name is already in the list");
            }
            else
            {
                ht.Add("008", "Visal Pateker");
            }
            // Get a collection of the keys.
            ICollection key = ht.Keys;
            foreach (string k in key)
            {
                Console.WriteLine(k + ": " + ht[k]);
            }
            Console.ReadKey();
        }
    }
}