Arrays, Lists, and Collections

# CHAPTER 6

Arrays, Lists, and Collections #

1. Introduction #

2. Learning Objectives #

• Declare, initialize, and access data in an Array.

• Understand the Zero-Index rule of programming.

• Use a List<T> to create dynamic, resizable collections.

• Use a Dictionary<TKey, TValue> for ultra-fast data lookups.

• Iterate through collections using foreach loops.

3. Arrays (The Fixed Box) #

• *Limitation:* You must define exactly how big the array is when you create it. It cannot grow or shrink later!

• Arrays are incredibly fast, making them perfect for fixed data (e.g., 4 players in a split-screen game, or 6 slots in a revolver).

// Create an array that holds exactly 3 strings
string[] inventory = new string[3];

// Add items (Programming starts counting at Zero!)
inventory[0] = "Sword";
inventory[1] = "Shield";
inventory[2] = "Potion";

Console.WriteLine("Equipped: " + inventory[0]); // Prints "Sword"

4. Lists (The Expanding Backpack) #

• *Requirement:* You must add using System.Collections.Generic; at the top of your script.

List<string> backpack = new List<string>();

backpack.Add("Sword");
backpack.Add("Health Potion");
backpack.Remove("Sword"); // The list automatically shrinks!

Console.WriteLine("Items in bag: " + backpack.Count);

5. Dictionaries (The Key-Value Map) #

// Key is a String (Enemy Name), Value is an Int (Health)
Dictionary<string, int> bestiary = new Dictionary<string, int>();

bestiary.Add("Goblin", 50);
bestiary.Add("Dragon", 5000);

// Ultra-fast lookup!
Console.WriteLine("Dragon HP: " + bestiary["Dragon"]);

6. The foreach Loop #

List<string> weapons = new List<string>() { "Axe", "Bow", "Dagger" };

foreach (string w in weapons)
{
    Console.WriteLine("You have a: " + w);
}

7. Visual Learning: The Index Concept #

[ ARRAY: string[] inventory = new string[4]; ]

Index:    [0]         [1]         [2]         [3]
Data:  [ "Sword" ] [ "Bow" ]   [ NULL ]    [ NULL ]

*Note: If you try to access inventory[4], the game will instantly crash with an "Index Out Of Bounds" exception!*

8. Best Practices #

• Use Lists for Gameplay, Arrays for Performance: If you are spawning and deleting enemies constantly, use a List. If you are building a voxel engine (like Minecraft) holding exactly 16x16x16 blocks, use an Array. Arrays are slightly faster for the CPU to read.

9. Common Mistakes #

• Index Out of Range Exception: The most common bug in programming. If an Array has 3 items, the slots are 0, 1, 2. If you ask the computer for slot 3, it looks outside the allocated memory and crashes the program. *Always remember: Length is 3, but the highest Index is 2!*

10. Mini Project: Build an RPG Inventory #

1. 1. Open your Console project. Write the following:

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // 1. Create a dynamic List
        List<string> inventory = new List<string>();

        // 2. Player loots a chest
        Console.WriteLine("Looting chest...");
        inventory.Add("Iron Sword");
        inventory.Add("Health Potion");
        inventory.Add("Gold Coin");

        // 3. Player drinks a potion
        Console.WriteLine("Drinking potion...");
        inventory.Remove("Health Potion");

        // 4. Display Inventory
        Console.WriteLine("\n--- CURRENT INVENTORY ---");
        foreach (string item in inventory)
        {
            Console.WriteLine("- " + item);
        }
        Console.WriteLine("Total items: " + inventory.Count);
    }
}

1. 2. Press Play. Watch the dynamic addition, removal, and rendering of the data!

11. Practice Exercises #

1. 1. What namespace must be included at the top of your script to use List<T> and Dictionary<TKey, TValue>?

1. 2. If you declare int[] scores = new int[5];, what is the exact index number of the very last slot in that array?

12. MCQs with Answers #

13. Interview Questions #

• Q: Explain the fundamental difference in memory allocation between an Array and a List<T> in C#. When would you explicitly choose an Array over a List?

• Q: Walk me through the concept of "Zero-Index" arrays. Why does array.Length return a number that is 1 higher than the maximum readable index?

• Q: A game requires you to instantly look up the required crafting materials for an item simply by providing the item's name (e.g., passing "Iron Sword" instantly returns "2 Iron, 1 Wood"). Which Collection is best suited for this, and why?

14. FAQs #

15. Summary #

16. Next Chapter Recommendation #