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Dictionary in C#

Educative Answers Team

A dictionary is a data structure in C# that is similar to the hash-table (a collection used to store key-value pairs). In a dictionary, we cannot have duplicate or null keys, but we can have duplicate or null values.

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Syntax

The first argument specifies the key type and the second is for the value type.

Dictionary <dataType, dataType> dictionary = new Dictionary<dataType, dataType>();

Remember: Dictionary collection is implemented in the class System.Collection.Generics.

Basic methods

Method Description
1.Add(key, value) Used to insert a key-value pair in a dictionary.
2.Remove(key) Used to remove a pair with a specified key.
3.ConatinsKey(key) Used to check whether or not a specified key exists in the dictionary.
4.ConatinsValue(value) Used to check whether or not a specified value exists in the dictionary.
5.Clear() Used to remove all the pairs from the dictionary.

Code

using System; 
using System.Collections.Generic; 

class DictionaryTesting
{
    static void Main()
    {
        Dictionary<int, string> dictionary = new Dictionary<int, string>();

        // Add(key, value) Method
        dictionary.Add(1,"John");
        dictionary.Add(2,"Cassy");
        dictionary.Add(3,"Peter");
        dictionary.Add(4,"Luis");
        dictionary.Add(5,"Flash");

        // Printing dictionary
        System.Console.WriteLine("Dictionary after adding pair:");
        foreach(KeyValuePair<int, string> temp in dictionary) 
          { 
            Console.WriteLine("Key {0} and Value {1}", temp.Key, temp.Value); 
          }
        
        // Remove(key) Method
        dictionary.Remove(4);        
        
        // Printing dictionary
        System.Console.WriteLine("Dictionary after removing pair with key 4:");
        foreach(KeyValuePair<int, string> temp in dictionary) 
          { 
            Console.WriteLine("Key {0} and Value {1}", temp.Key, temp.Value); 
          }

        // ConatinsKey(key) Method
        System.Console.WriteLine("Dictionary has any pair with the key = 5?");
        System.Console.WriteLine(dictionary.ContainsKey(5));
    }
}
After execution, scroll down to see the complete output.

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