Array and Arraylist in C#

In C#, both arrays and ArrayLists are used to store and manipulate collections of objects, but they differ in their behavior and features. Let's explore the differences between arrays and ArrayLists in detail, along with examples:


  1. Definition: An array is a fixed-size data structure that stores a collection of elements of the same type. The size of an array is determined at compile time and remains constant throughout its lifetime.
  2. Initialization: Arrays can be initialized using the array initializer syntax or by specifying the size and then assigning values to individual elements.
  3. Element Access: Elements in an array are accessed by their index, starting from 0.
  4. Type Safety: Arrays provide type safety, meaning that the type of elements stored in the array is known and enforced by the compiler.
  5. Fixed Size: Arrays have a fixed size, which means the size cannot be changed once the array is created.
  6. Performance: Arrays offer better performance in terms of memory usage and element access compared to ArrayLists.
int[] numbers = new int[3]; // Declaration and allocation of an integer array numbers[0] = 1; // Assigning value to the first element numbers[1] = 2; // Assigning value to the second element numbers[2] = 3; // Assigning value to the third element


  1. Definition: An ArrayList is a dynamic data structure that can store a collection of objects of any type. It automatically adjusts its size as elements are added or removed.
  2. Element Access: Elements in an ArrayList are accessed using indexing, similar to arrays.
  3. Initialization: ArrayLists can be initialized using the ArrayList constructor or by using the ArrayList initializer syntax in C# 3.0 and later versions.
  4. Type Safety: ArrayLists store objects of type object, which allows for storing elements of different types in the same ArrayList. This can lead to type-related issues at runtime, as explicit casting may be required when retrieving elements.
  5. Dynamic Size: ArrayLists can dynamically resize themselves to accommodate additional elements as needed. This flexibility allows for easy addition and removal of elements.
  6. Performance: ArrayLists may have a slight performance overhead compared to arrays due to the boxing and unboxing operations required when storing and retrieving elements of value types.
ArrayList list = new ArrayList(); // Declaration and instantiation of an ArrayList list.Add(1); // Adding an integer element list.Add("Hello"); // Adding a string element list.Add(true); // Adding a boolean element

In the above example, the ArrayList can store elements of different types without explicitly specifying the element type, as it stores objects of type object.


Arrays provide a fixed-size collection with better performance and type safety, whereas ArrayLists offer dynamic resizing and the ability to store objects of different types. The choice between arrays and ArrayLists depends on the specific requirements of the application, such as the need for a fixed-size collection, type safety, or dynamic resizing capabilities.