Lesson 2 — Values and variables

You are here

1. Your first program ✓
2. Values and variables ←
3. Making decisions
4. Repeating things
5. Functions
6. Lists and hashes
7. Strings
8. Organizing programs
9. Classes

What are we learning?

A value is a piece of data: text, a number, true/false, and so on.

A variable is a name that refers to a value, so you can use that value again.

The idea in ordinary language

Think of a labeled box:

• The label is the variable name (name).
• What is inside the box is the value ("Echo").

Smallest useful example

name: str = "Echo";
say(name);

Output

Echo

Line by line

1. name — the label (variable name).
2. : str — this name holds text. In Echo, str means text (short for “string”).
3. = "Echo" — put the text Echo in that name.
4. ; — end of the instruction.
5. say(name); — print whatever name currently refers to (not the word name, but the value).

Why : str?

Echo requires a type on a new variable. A type is a short label for the kind of value allowed. You will see str (text), int (whole numbers), bool (true / false), and others later.

More kinds of values

title: str = "Echo";
users: int = 42;
ready: bool = true;

say(title, users, ready);

Output

Echo 42 true

• int — whole numbers (1, 42, -3)
• bool — true or false

Changing a value

After you declare a name, you can give it a new value of the same kind:

count: int = 1;
count = 2;
say(count);

Output

2

Notice the second line has no : int — the name already exists.

Try it — change the value

Start from:

name: str = "Echo";
say(name);

Change "Echo" to your name and run again.

Predict it

What will this print?

city: str = "Paris";
say(city);

Show answer

Paris

Fix it — name used before it exists

This fails:

count = 1;

Echo needs the type the first time:

count: int = 1;

Deeper (later)

Unions, destructuring, const, dynamic, and class types are covered in Variables and Types (full). Skip that until you finish the Learn path.

Next

→ Lesson 3 — Making decisions