How to Check if a Key Exists in a Dictionary in C# - Step by Step Examples

How to Check if a Key Exists in a Dictionary in C# ?

Answer

To check if a key exists in a dictionary in C#, you can use the `ContainsKey` method of the `Dictionary` class from the `System.Collections.Generic` namespace.

✐ Examples

1 Checking if a Key Exists Using the `ContainsKey` Method

We can check if a key exists in a dictionary in C# using the `ContainsKey` method. This example demonstrates how to check for the presence of a key and print a message based on the result.

For example,

We start by including the necessary namespace: using System.Collections.Generic;.
We declare and initialize a dictionary named myDictionary with integer keys and string values.
We use the `ContainsKey` method to check if a key exists in the dictionary.
We print a message based on whether the key exists or not.

C# Program

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Declare and initialize a dictionary
        Dictionary<int, string> myDictionary = new Dictionary<int, string>
        {
            {1, "One"},
            {2, "Two"},
            {3, "Three"}
        };

        // Key to check
        int keyToCheck = 2;

        // Check if the key exists using the ContainsKey method
        if (myDictionary.ContainsKey(keyToCheck))
        {
            Console.WriteLine("Key {0} exists in the dictionary.", keyToCheck);
        }
        else
        {
            Console.WriteLine("Key {0} does not exist in the dictionary.", keyToCheck);
        }
    }
}

Output

Key 2 exists in the dictionary.

2 Checking if a Key Does Not Exist Using the `ContainsKey` Method

We can check if a key does not exist in a dictionary in C# using the `ContainsKey` method. This example demonstrates how to check for the absence of a key and print a message based on the result.

For example,

We start by including the necessary namespace: using System.Collections.Generic;.
We declare and initialize a dictionary named myDictionary with integer keys and string values.
We use the `ContainsKey` method to check if a key does not exist in the dictionary.
We print a message based on whether the key exists or not.

C# Program

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Declare and initialize a dictionary
        Dictionary<int, string> myDictionary = new Dictionary<int, string>
        {
            {1, "One"},
            {2, "Two"},
            {3, "Three"}
        };

        // Key to check
        int keyToCheck = 4;

        // Check if the key does not exist using the ContainsKey method
        if (!myDictionary.ContainsKey(keyToCheck))
        {
            Console.WriteLine("Key {0} does not exist in the dictionary.", keyToCheck);
        }
        else
        {
            Console.WriteLine("Key {0} exists in the dictionary.", keyToCheck);
        }
    }
}

Output

Key 4 does not exist in the dictionary.

Summary

In this tutorial, we learned How to Check if a Key Exists in a Dictionary in C# language with well detailed examples.

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How to Check if a Key Exists in a Dictionary in C# - Step by Step Examples