Add key-value pair in C# Dictionary

To add key-value pairs in C# Dictionary, you can use several methods. The Dictionary class provides multiple ways to insert elements, each with its own advantages for different scenarios.

Syntax

Following are the main syntaxes for adding key-value pairs to a Dictionary −

// Using Add() method with separate key and value
dictionary.Add(key, value);

// Using Add() method with KeyValuePair
dictionary.Add(new KeyValuePair<TKey, TValue>(key, value));

// Using indexer syntax
dictionary[key] = value;

Using Add() Method with Key and Value

The most common approach is using the Add() method with separate key and value parameters −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Dictionary<int, string> products = new Dictionary<int, string>();
      
      // Add key-value pairs using Add() method
      products.Add(1, "TVs");
      products.Add(2, "Appliances");
      products.Add(3, "Mobile");
      products.Add(4, "Laptop");
      
      // Display the dictionary
      foreach (KeyValuePair<int, string> item in products) {
         Console.WriteLine("Key = {0}, Value = {1}", item.Key, item.Value);
      }
   }
}

The output of the above code is −

Key = 1, Value = TVs
Key = 2, Value = Appliances
Key = 3, Value = Mobile
Key = 4, Value = Laptop

Using Add() Method with KeyValuePair

You can also add elements using the KeyValuePair structure −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      IDictionary<int, string> d = new Dictionary<int, string>();
      
      d.Add(new KeyValuePair<int, string>(1, "TVs"));
      d.Add(new KeyValuePair<int, string>(2, "Appliances"));
      d.Add(new KeyValuePair<int, string>(3, "Mobile"));
      d.Add(new KeyValuePair<int, string>(4, "Tablet"));
      d.Add(new KeyValuePair<int, string>(5, "Laptop"));
      
      foreach (KeyValuePair<int, string> ele in d) {
         Console.WriteLine("Key = {0}, Value = {1}", ele.Key, ele.Value);
      }
   }
}

The output of the above code is −

Key = 1, Value = TVs
Key = 2, Value = Appliances
Key = 3, Value = Mobile
Key = 4, Value = Tablet
Key = 5, Value = Laptop

Using Indexer Syntax

The indexer syntax provides a convenient way to add or update key-value pairs −

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Dictionary<string, int> ages = new Dictionary<string, int>();
      
      // Add using indexer syntax
      ages["Alice"] = 25;
      ages["Bob"] = 30;
      ages["Charlie"] = 35;
      
      // Update existing key (no exception thrown)
      ages["Alice"] = 26;
      
      foreach (var person in ages) {
         Console.WriteLine("{0} is {1} years old", person.Key, person.Value);
      }
   }
}

The output of the above code is −

Alice is 26 years old
Bob is 30 years old
Charlie is 35 years old

Comparison of Methods

Conclusion

C# Dictionary offers multiple methods to add key-value pairs: Add() method for strict insertion, KeyValuePair approach for structured data, and indexer syntax for flexible add-or-update operations. Choose the method based on whether you need duplicate key protection or update capability.