How to Set a Default Value for a Key in a Dictionary in C#

How to Set a Default Value for a Key in a Dictionary in C# ?

Answer

To set a default value for a key in a dictionary in C#, you can check if the key exists using the `ContainsKey` method. If the key does not exist, you can add the key with a default value.

✐ Examples

1 Setting a Default Value for a Key Using `ContainsKey` Method

We can set a default value for a key in a dictionary in C# using the `ContainsKey` method. This example demonstrates how to check if a key exists and set a default value if it does not.

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 check if a key exists using the `ContainsKey` method.
If the key does not exist, we set a default value for the key.
We print the dictionary contents to verify the key-value pairs.

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>();

        // Key to check
        int keyToCheck = 1;

        // Default value to set if key does not exist
        string defaultValue = "Default";

        // Check if the key exists and set default value if it does not
        if (!myDictionary.ContainsKey(keyToCheck))
        {
            myDictionary[keyToCheck] = defaultValue;
        }

        // 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: Default

2 Setting a Default Value for Multiple Keys Using a Helper Method

We can create a helper method to set a default value for multiple keys in a dictionary in C#. This example demonstrates how to use a helper method to set default values for keys.

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 create a helper method named SetDefaultValue to set default values for keys.
We use the helper method to set default values for multiple keys.
We print the dictionary contents to verify the key-value pairs.

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>();

        // Helper method to set default value
        void SetDefaultValue(Dictionary<int, string> dict, int key, string defaultValue)
        {
            if (!dict.ContainsKey(key))
            {
                dict[key] = defaultValue;
            }
        }

        // Set default values for multiple keys
        SetDefaultValue(myDictionary, 1, "DefaultOne");
        SetDefaultValue(myDictionary, 2, "DefaultTwo");

        // 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: DefaultOne
Key: 2, Value: DefaultTwo

Summary

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

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