What is the Difference Between an ArrayList and a Dictionary in C#?

An ArrayList in C# is a collection of elements that are stored in a sequential order, while a Dictionary is a collection of key-value pairs.

ArrayList

• Sequential Order: Elements in an ArrayList are stored in the order they are added.

• Data Type: An ArrayList can store elements of any data type.

• Access: You can access elements in an ArrayList using their index, starting from 0.

• Example:

    ArrayList names = new ArrayList();
    names.Add("John");
    names.Add("Jane");
    names.Add("Peter");
  
    Console.WriteLine(names[1]); // Output: Jane

Dictionary

• Key-Value Pairs: A Dictionary stores data in key-value pairs. Each key must be unique and is used to access its corresponding value.

• Data Type: You can specify the data types for both the keys and values.

• Access: You can access values in a Dictionary using their corresponding keys.

• Example:

    Dictionary<string, int> ages = new Dictionary<string, int>();
    ages.Add("John", 30);
    ages.Add("Jane", 25);
    ages.Add("Peter", 40);
  
    Console.WriteLine(ages["Jane"]); // Output: 25

Key Differences

Practical Insights

• Use an ArrayList when you need to store a collection of data in a specific order and access elements by their index.
• Use a Dictionary when you need to store data in key-value pairs and access values using their corresponding keys.