C# | Dictionary.ContainsKey() Method

This method is used to check whether the Dictionary<TKey,TValue> contains the specified key or not.

Syntax:

public bool ContainsKey (TKey key);

Here, the key is the Key which is to be located in the Dictionary.

Return Value: This method will return true if the Dictionary contains an element with the specified key otherwise, it returns false.

Exception: This method will give ArgumentNullException if the key is null.

Below are the programs to illustrate the use of Dictionary<TKey,TValue>.ContainsKey() Method:

Example 1:

// C# code to check if a key is
// present or not in a 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");

        // Checking for Key "India"
        if (myDict.ContainsKey("India"))
            Console.WriteLine("Key : India is present");

        else
            Console.WriteLine("Key : India is absent");
    }
}

Output:

Key : India is present

Example 2:

// C# code to check if a key is
// present or not in a 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");

        // Checking for Key "USA"
        if (myDict.ContainsKey("USA"))
            Console.WriteLine("Key : USA is present");

        else
            Console.WriteLine("Key : USA is absent");
    }
}

Output:

Key : USA is absent

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.containskey?view=netframework-4.7.2