Lists & Collections | Learn to Write Code

A list holds many values in one ordered group

A list stores several values together, in order, under one name.

Each value has a position in the list called an index. Indexes start counting at 0, so the first item is at index 0, not 1.

Store many related values in one list.
Reach a single value by its index position.
Add new values to the end of a list.
Visit every item with FOR EACH.

Think of a numbered row of mailboxes: mailbox 0 is the first one, not the "zeroth" one.

Try it: Given a list of colors ["Red", "Green", "Blue"], which index would get you "Green"? What would the list contain after you ADD "Yellow" to it?

Create a list, read an item, then loop over all of them

We look up the first fruit by index, add a new fruit to the end, then visit every fruit in order.

Pseudocode

CREATE fruits AS LIST WITH "Apple", "Banana", "Cherry"
SHOW ITEM 0 OF fruits

ADD "Date" TO fruits
SHOW LENGTH OF fruits

FOR EACH fruit IN fruits
    SHOW fruit
END FOR

The same idea in Python

Python lists index from 0, append with .append(), and support for...in directly over the list.

Python

fruits = ["Apple", "Banana", "Cherry"]
print(fruits[0])

fruits.append("Date")
print(len(fruits))

for fruit in fruits:
    print(fruit)

The same idea in JavaScript

JavaScript arrays use the same 0-based indexing, push() to add, and for...of to visit each item.

JavaScript

const fruits = ["Apple", "Banana", "Cherry"];
console.log(fruits[0]);

fruits.push("Date");
console.log(fruits.length);

for (const fruit of fruits) {
    console.log(fruit);
}

The same idea in C#

C# uses a List<string> for a growable collection, Add() to append, and foreach to visit each item.

List<string> fruits = new List<string> { "Apple", "Banana", "Cherry" };
Console.WriteLine(fruits[0]);

fruits.Add("Date");
Console.WriteLine(fruits.Count);

foreach (string fruit in fruits)
{
    Console.WriteLine(fruit);
}

The same idea in Java

Java uses a List of String, get() to read by index, add() to append, and an enhanced for loop to visit each item.

Java

List<String> fruits = new ArrayList<>(List.of("Apple", "Banana", "Cherry"));
System.out.println(fruits.get(0));

fruits.add("Date");
System.out.println(fruits.size());

for (String fruit : fruits) {
    System.out.println(fruit);
}

The same idea in C++

C++ uses a std::vector for a growable list, push_back() to append, and a range-based for loop to visit each item.

C++

std::vector<std::string> fruits = {"Apple", "Banana", "Cherry"};
std::cout << fruits[0] << '\n';

fruits.push_back("Date");
std::cout << fruits.size() << '\n';

for (const std::string& fruit : fruits)
{
    std::cout << fruit << '\n';
}