Working with Hashtable and Dictionary in C#

Csharp Programming Server Side Programming

Hashtable

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.

Some of the commonly used methods in Hashtable class are −

Sr.No.	Method & Description
1	public virtual void Add(object key, object value); Adds an element with the specified key and value into the Hashtable.
2	public virtual void Clear(); Removes all elements from the Hashtable.
3	public virtual bool ContainsKey(object key); Determines whether the Hashtable contains a specific key.
4	public virtual bool ContainsValue(object value); Determines whether the Hashtable contains a specific value.

The following is an example showing the usage of Hashtable class in C# −

Example

Live Demo

using System;
using System.Collections;

namespace Demo {
   class Program {
      static void Main(string[] args) {
         Hashtable ht = new Hashtable();

         ht.Add("D01", "Finance");
         ht.Add("D02", "HR");
         ht.Add("D03", "Operations");

         if (ht.ContainsValue("Marketing")) {
            Console.WriteLine("This department name is already in the list");
         } else {
            ht.Add("D04", "Marketing");
         }

         ICollection key = ht.Keys;

         foreach (string k in key) {
            Console.WriteLine(k + ": " + ht[k]);
         }
         Console.ReadKey();
      }
   }
}

Output

D04: Marketing
D02: HR
D03: Operations
D01: Finance

Dictionary

Dictionary is a collection of keys and values in C#. Dictionary <TKey, TValue> is included in the System.Collection.Generics namespace.

The following are the methods −

Sr.No.	Methods & Description
1	Add Add key-value pairs in Dictionary
2	Clear() Remove all keays and values
3	Remove Removes the element with the specified key.
4	ContainsKey Checks whether the specified key exists in Dictionary <TKey, TValue>.
5	ContainsValue Checks whether the specified key value exists in Dictionary <TKey, TValue>.
6	Count Count the number of key-valu pairs.
7	Clear Removes all the elements from Dictionary <TKey, TValue>.

Let us see how to add elements into a Dictionary and display the count −

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {

      IDictionary <int, int> d = new Dictionary <int, int> ();
      d.Add(1,44);
      d.Add(2,34);
      d.Add(3,66);
      d.Add(4,47);
      d.Add(5,76);

      Console.WriteLine(d.Count);
   }
}