C# | Dictionary.Item[] Property

Last Updated : 11 Jul, 2025
This property is used to get or set the value associated with the specified key in the Dictionary. Syntax: 
public TValue this[TKey key] { get; set; }
Here, key is the Key of the value to get or set. Property Value: It is the value associated with the specified key. If the specified key is not found, a get operation throws a KeyNotFoundException, and a set operation creates a new element with the specified key. Exceptions:
  • ArgumentNullException: If the key is null.
  • KeyNotFoundException: If the property is retrieved and key does not exist in the collection.
Example: csharp 
// C# code to get or set the value
// associated with the specified key
using System;
using System.Collections;
using System.Collections.Generic;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating a Dictionary named myDict
        Dictionary<string, string> myDict = new Dictionary<string, string>();

        // Adding key/value pairs in myDict
        myDict.Add("Australia", "Canberra");
        myDict.Add("Belgium", "Brussels");
        myDict.Add("Netherlands", "Amsterdam");
        myDict.Add("China", "Beijing");
        myDict.Add("Russia", "Moscow");
        myDict.Add("India", "New Delhi");

        // Displaying the key/value pairs in myDict
        foreach(KeyValuePair<string, string> k in myDict)
        {
            Console.WriteLine("Key = {0}, Value = {1}",
                              k.Key, k.Value);
        }

        // Displaying the value associated
        // with key "Russia"
        Console.Write("\nValue associated with Russia: ");
        Console.Write(myDict["Russia"]);

        // Setting the value associated with key "Russia"
        myDict["Russia"] = "Saint Petersburg";

        // Displaying the value associated
        // with key "Russia"
        Console.Write("\n\nValue associated with Russia After Setting: ");
        Console.Write(myDict["Russia"]);

        // Displaying the value associated
        // with key "India"
        Console.Write("\n\nValue associated with India: ");
        Console.Write(myDict["India"]);

        // Setting the value associated with key "India"
        myDict["India"] = "Mumbai";

        // Displaying the value associated
        // with key "India"
        Console.Write("\n\nValue associated with India After Setting: ");
        Console.Write(myDict["India"]);
        Console.WriteLine("\n");

        // Displaying the key/value pairs in myDict
        foreach(KeyValuePair<string, string> k1 in myDict)
        {
            Console.WriteLine("Key = {0}, Value = {1}",
                              k1.Key, k1.Value);
        }
    }
}
Output: 
Key = Australia, Value = Canberra
Key = Belgium, Value = Brussels
Key = Netherlands, Value = Amsterdam
Key = China, Value = Beijing
Key = Russia, Value = Moscow
Key = India, Value = New Delhi

Value associated with Russia: Moscow

Value associated with Russia After Setting: Saint Petersburg

Value associated with India: New Delhi

Value associated with India After Setting: Mumbai

Key = Australia, Value = Canberra
Key = Belgium, Value = Brussels
Key = Netherlands, Value = Amsterdam
Key = China, Value = Beijing
Key = Russia, Value = Saint Petersburg
Key = India, Value = Mumbai
Reference:
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