Week 3 - Data Structures: Arrays and Lists

Learning Goals

• Store multiple values using a one-dimensional array.
• Use a List<T> to store data that can grow and shrink.
• Access items by index.
• Understand the difference between an array and a list.

Key Concepts

One-Dimensional Arrays

An array holds a fixed number of items, all the same type.

string[] items = { "Milk", "Bread", "Eggs" };

Console.WriteLine(items[0]);
Console.WriteLine(items[2]);

items[1] = "Butter";

Console.WriteLine(items.Length);

Lists

A List<T> can grow and shrink at runtime.

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

shoppingList.Add("Apple");
shoppingList.Add("Orange");
shoppingList.Add("Banana");

shoppingList.Remove("Orange");

Console.WriteLine(shoppingList[0]);
Console.WriteLine(shoppingList.Count);

foreach (string item in shoppingList)
{
    Console.WriteLine(item);
}

Records Through Parallel Arrays

When each item needs multiple pieces of data, you can use parallel arrays.

string[] productNames = { "Milk", "Bread", "Eggs" };
double[] productPrices = { 2.10, 3.50, 4.00 };
int[] productStock = { 12, 0, 7 };

Console.WriteLine($"{productNames[1]} costs ${productPrices[1]}");

Your Task

Create a new Console App called Week3_DataStructures.

Write a program that:

1. Uses parallel arrays to store 4 shop products: name, price and stock quantity.
2. Uses a for loop to display all products in a table format.
3. Calculates and displays the total value of all stock.

Expected Output

--- Inventory ---
Milk        $2.10   x12   = $25.20
Bread       $3.50   x0    = $0.00
Eggs        $4.00   x7    = $28.00
Cola        $3.00   x5    = $15.00

Total stock value: $68.20

Extension

• Create a List<string> called outOfStock and add the names of any items with quantity 0 during the loop.
• After the loop, display the out-of-stock list.

Common Mistakes to Avoid

• accessing an index that does not exist
• using .Length on a List<T> instead of .Count
• forgetting that parallel arrays must stay in sync