Variables

A variable is a name that refers to a value, so you can use or change that value later.

Real-world analogy: a variable is like a sticky label. You write a name on the label and stick it on a value. You can later peel the label off and stick it on a different value.

Syntax

name = "Ada"

There's no keyword (like let or var) and no type. Assigning a value creates the variable.

Example

city = "Lagos"
age = 25
puts city
puts age

age = 26
puts age

age = age + 1
puts age

Expected output

Lagos
25
26
27

age = age + 1 reads the current value (26), adds one, and makes age refer to the result. The shorter form age += 1 does the same.

Naming rules

• Use snake_case: lowercase words joined by underscores, like first_name or total_price.
• Names can contain letters, digits, and underscores, but can't start with a digit.
• Choose descriptive names: total_price explains itself; tp doesn't.

Constants

A name that starts with a capital letter is a constant — a value meant to stay the same. By convention, constants are written in SCREAMING_SNAKE_CASE:

MAX_PLAYERS = 4

Ruby lets you reassign a constant but prints a warning (warning: already initialized constant MAX_PLAYERS) — treat that warning as a bug.

Common mistakes

• Using a variable before assigning it: undefined local variable or method 'score' for main (NameError).
• Mixing up Age and age — the capitalized one is a constant, not the same variable.

Practice

Create a variable apples set to 5. Add 3 to it using +=, then print I have 8 apples.

Hint: you can join text and a number with interpolation — "I have #{apples} apples". The Strings lesson explains how it works.

apples = 5
apples += 3
puts "I have #{apples} apples"