C# | Dictionary.Add() Method Last Updated : 11 Jul, 2025 Summarize Comments Improve Suggest changes Share Like Article Like Report Dictionary<TKey,TValue>.Add() Method is used to add a specified key and value to the dictionary. Syntax: public void Add (TKey key, TValue value); Parameters: key: It is the key of the element to add. value: It is the value of the element to add. The value can be null for reference types. Exceptions: ArgumentNullException : If the key is null. ArgumentException : If an element with the same key already exists in the Dictionary. Below are the programs to illustrate the use of Dictionary<TKey,TValue>.Add() Method: Example 1: csharp // C# code to add the specified key // and value into the Dictionary using System; using System.Collections.Generic; class GFG { // Driver code public static void Main() { // Create a new dictionary // of strings, with string keys. 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"); // To get count of key/value // pairs in myDict Console.WriteLine("Total key/value pairs in"+ " myDict are : " + myDict.Count); // Displaying the key/value // pairs in myDict Console.WriteLine("The key/value pairs"+ " in myDict are : "); foreach(KeyValuePair<string, string> kvp in myDict) { Console.WriteLine("Key = {0}, Value = {1}", kvp.Key, kvp.Value); } } } Output: Total key/value pairs in myDict are : 6 The key/value pairs in myDict are : 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 Example 2: csharp // C# code to add the specified // key and value into the Dictionary using System; using System.Collections.Generic; class GFG { // Driver code public static void Main() { // Create a new dictionary of // strings, with string keys. 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"); // The Add method throws an // exception if the new key is // already in the dictionary. try { myDict.Add("Russia", "Moscow"); } catch (ArgumentException) { Console.WriteLine("An element with Key "+ "= \"Russia\" already exists."); } } } Output: An element with Key = "Russia" already exists. Note: A key cannot be null, but a value can be if TValue is a reference type. If Count is less than the capacity, this method approaches an O(1) operation. If the capacity must be increased to accommodate the new element, this method becomes an O(n) operation, where n is Count. Reference: https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.add?view=netframework-4.7.2 Comment More infoAdvertise with us Next Article C# Dictionary R rupesh_rao Follow Improve Article Tags : C# CSharp-method CSharp-Generic-Namespace CSharp Dictionary Class Similar Reads C# Dictionary Dictionary in C# is a generic collection that stores key-value pairs. The working of Dictionary is quite similar to the non-generic hashtable. The advantage of a Dictionary is, that it is a generic type. A dictionary is defined under System.Collections.Generic namespace. It is dynamic in nature mean 5 min read C# Dictionary Dictionary in C# is a generic collection that stores key-value pairs. The working of Dictionary is quite similar to the non-generic hashtable. The advantage of a Dictionary is, that it is a generic type. A dictionary is defined under System.Collections.Generic namespace. It is dynamic in nature mean 5 min read C# | Dictionary.Item[] Property 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, 2 min read C# | Dictionary.Count Property This property is used to get the number of key/value pairs contained in the Dictionary. Syntax: public int Count { get; } Return Value : The number of key/value pairs contained in the Dictionary. Below are the programs to illustrate the use of above-discussed property: Example 1: csharp // C# code t 2 min read C# Dictionary Class In C#, the Dictionary class is the part of the System.Collections.Generic namespace. It is a Collection that stores Key-value pairs. Each key in the dictionary is unique and each key maps to a single value.In Dictionary, each entry consists of a key and its associated value.It provides constant time 7 min read C# | SortedDictionary.Add() Method This is used to add a specified key and value to the sorted dictionary. The elements are sorted according to TKey. Syntax: public void Add (TKey key, TValue value); Parameters: key: It is the key of the element to add. value: It is the value of the element to add. The value can be null for reference 3 min read Like