Operators

An operator is a symbol that performs an action on values, like + for adding or > for comparing.

Arithmetic

+, -, *, /, % (remainder), ** (power) — covered in the Numbers lesson.

Assignment shortcuts

score = 10
score += 5    # score = score + 5
score -= 2    # score = score - 2
score *= 2    # score = score * 2
p score

26

||= assigns only if the variable is currently nil or false — a very common Ruby idiom for defaults:

nickname = nil
nickname ||= "Guest"
p nickname

"Guest"

Comparison

The spaceship operator returns -1 if the left side is smaller, 0 if they're equal, and 1 if it's bigger. Ruby uses it for sorting.

Logical

age = 20
has_ticket = true

p age >= 18 && has_ticket
p age < 13 || age > 65
p !has_ticket

true
false
false

• && (and) is true only if both sides are true.
• || (or) is true if either side is true.
• ! (not) flips true and false.

Ruby also has the words and, or, and not, but they have lower precedence than = and behave surprisingly in assignments. Stick to &&, ||, and ! in conditions.

Common mistakes

• Writing = (assignment) instead of == (comparison) in a condition. if x = 5 assigns 5 and is always true; Ruby prints a warning.

Practice

A shop gives free delivery when an order is over 50, or when the customer is a member. With total = 42 and member = true, print whether delivery is free.

total = 42
member = true
p total > 50 || member

true