Arrays And Collections

Lesson 2.5: Arrays and Collections: Storing Multiple Items

Up until now, you've worked with variables that hold a single value at a time. In this lesson, you'll learn about two powerful ways to store collections of data: arrays and lists.

Arrays: Fixed-Size Collections

What Are They? An array is a container that can hold a fixed number of elements of the same data type. Think of it like a row of boxes, where each box can store one item (e.g., numbers, strings, or other types).

Why Use Arrays?

Organized Storage: Group related data together.

Efficient Access: Quickly access elements by their index (position).

Perform Operations: Easily sort, search, or manipulate the entire collection.

Declaring an Array:

C#

int[] numbers = new int[5]; // Creates an array to hold 5 integers

string[] names = new string[3]; // Creates an array to hold 3 strings

Initializing an Array:

C#

int[] numbers = new int[] { 5, 10, 15, 20, 25 }; // Initialization at declaration

string[] names = { "Alice", "Bob", "Charlie" };   // Shorter initialization syntax

Use code with caution.

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Accessing Array Elements:

Use square brackets [] to access elements by their index (starting from 0):

C#

numbers[0] = 12;  // Set the first element (index 0) to 12

string secondName = names[1]; // Get the second element (index 1)

Lists: Flexible Collections

What Are They? Lists are similar to arrays, but they can grow or shrink in size dynamically. This makes them more flexible when you don't know how many elements you'll need.

Why Use Lists?

Dynamic Size: Add or remove elements easily.

Built-in Methods: Many helpful methods for sorting, searching, inserting, and removing elements.

Declaring and Initializing a List:

C#

using System.Collections.Generic; // Required for using lists

List<int> numbers = new List<int>(); // Create an empty list of integers

numbers.Add(5); // Add elements to the list

numbers.Add(10);

Accessing List Elements:

Similar to arrays, use square brackets [] to access elements by index:

C#

int firstNumber = numbers[0];

Important Considerations

Array Size: Arrays have a fixed size, determined when you create them. You can't change the size later.

List Type: When creating a list, specify the data type of the elements it will hold (e.g., List<int> for integers).

Index Out of Range: Be careful not to try accessing elements at invalid indices (beyond the size of the array or list).

Example: Working with Arrays and Lists

C#

int[] ages = { 25, 30, 35 };

List<string> fruits = new List<string> { "apple", "banana", "orange" };

Console.WriteLine(ages[1]);    // Output: 30

Console.WriteLine(fruits[2]);   // Output: orange

fruits.Add("grape");           // Add a new fruit to the list

fruits.Remove("banana");       // Remove "banana" from the list

Going Further

Arrays and lists are just the tip of the iceberg. C# offers many other collection types for different use cases, such as:

Dictionary<TKey, TValue>: Store key-value pairs.

HashSet<T>: Store unique elements.

Queue<T> and Stack<T>: Implement specific data structures.

As you continue your C# journey, you'll discover how these powerful collections can help you solve a wide range of programming challenges!

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