How to Update the Value for a Key in a Dictionary in C#

How to Update the Value for a Key in a Dictionary in C# ?

Answer

To update the value for a key in a dictionary in C#, you can use the indexer to assign a new value to the key. If the key does not exist, it will be added to the dictionary with the specified value.

✐ Examples

1 Updating the Value for a Key Using the Indexer

We can update the value for a key in a dictionary in C# using the indexer. This example demonstrates how to update the value for an existing key and add a new key-value pair if the key does not exist.

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 update the value for an existing key using the indexer.
We add a new key-value pair using the indexer.
We print the dictionary contents to verify the updates.

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"}
        };

        // Update the value for an existing key
        myDictionary[2] = "Two Updated";

        // Add a new key-value pair
        myDictionary[4] = "Four";

        // Print the dictionary contents
        Console.WriteLine("Dictionary contents:");
        foreach (KeyValuePair<int, string> kvp in myDictionary)
        {
            Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
        }
    }
}

Output

Dictionary contents:
Key: 1, Value: One
Key: 2, Value: Two Updated
Key: 3, Value: Three
Key: 4, Value: Four

2 Updating the Value for a Key Using the `TryGetValue` Method

We can update the value for a key in a dictionary in C# using the `TryGetValue` method to check if the key exists before updating it. This example demonstrates how to safely update the value for an existing key.

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 `TryGetValue` method to check if a key exists.
If the key exists, we update its value.
We print the dictionary contents to verify the updates.

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 update
        int keyToUpdate = 2;

        // New value to set
        string newValue = "Two Updated";

        // Check if the key exists and update its value
        if (myDictionary.TryGetValue(keyToUpdate, out _))
        {
            myDictionary[keyToUpdate] = newValue;
        }

        // Print the dictionary contents
        Console.WriteLine("Dictionary contents:");
        foreach (KeyValuePair<int, string> kvp in myDictionary)
        {
            Console.WriteLine("Key: {0}, Value: {1}", kvp.Key, kvp.Value);
        }
    }
}

Output

Dictionary contents:
Key: 1, Value: One
Key: 2, Value: Two Updated
Key: 3, Value: Three

Summary

In this tutorial, we learned How to Update the Value for a Key in a Dictionary in C# language with well detailed examples.

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