meet it

A grows every time you add to it.

An array has a fixed size: you choose how many slots before you start. A List grows instead. Start it empty, then add as many items as you like. Lists live in a toolbox called System.Collections.Generic, so bring it in with a second using line.

List<string> pets = new List<string>(); makes an empty list of strings. The , < and >, hold the type of item the list keeps. .Add("cat") puts an item on the end, and its , pets.Count, says how many items it holds right now.

Read an item by its index, as with an array: pets[0]. You can also fill a list as you make it, with a : new List<string> { "cat", "dog" }. A list prints only its type, so use string.Join to see the items.

using System;
using System.Collections.Generic;

List<string> pets = new List<string>();
pets.Add("cat");
pets.Add("dog");
pets.Add("hamster");
Console.WriteLine(pets.Count);
Console.WriteLine(pets[0]);
Console.WriteLine(string.Join(", ", pets));

Arrays count with .Length, lists count with .Count.

guess first

The queue keeps growing. What will this show?

Guess before you run it. Wrong guesses are how you learn, and nothing is marked.

using System;
using System.Collections.Generic;

List<string> queue = new List<string> { "Amir", "Bella" };
Console.WriteLine(queue.Count);
queue.Add("Chen");
Console.WriteLine($"{queue[queue.Count - 1]} is last of {queue.Count}");

your turn

Your turn. Write a shopping list.

Put two things in the collection initialiser on line 4, then add a third on line 5. Press run to see how many things you need.

Your code

output

press run to see what happens

fix it

The guest count will not work. Can you fix it?

Broken code to fix

output

press run to see what happens

C# says CS1061 on line 5: a List has no Length. What does a list use to count its items?
Arrays count with Length, but lists count with a different word.
Change guests.Length to guests.Count on line 5, then press run.

nailed it

your list grows as you go. :D

A List grows every time you .Add an item.
.Count says how many items it holds.
Use string.Join to print the items themselves.

new words in your collection

List
angle brackets
Count
collection initialiser

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A List grows every time you add to it.

The queue keeps growing. What will this show?

Your turn. Write a shopping list.

The guest count will not work. Can you fix it?

your list grows as you go. :D

A grows every time you add to it.