case Expressions

A case expression compares one value against several possibilities — a cleaner alternative to a long if/elsif chain.

Syntax

case value
when option1
  # ...
when option2, option3
  # ...
else
  # none matched
end

Example

day = "Saturday"

case day
when "Saturday", "Sunday"
  puts "Weekend!"
when "Friday"
  puts "Almost weekend"
else
  puts "Weekday"
end

Expected output

Weekend!

A single when can list several values separated by commas.

Matching ranges and types

when isn't limited to exact equality. It can match a range of numbers or a class:

score = 84

grade = case score
        when 90..100 then "A"
        when 80...90 then "B"
        when 70...80 then "C"
        else "F"
        end

puts grade

value = 3.5
case value
when Integer then puts "a whole number"
when Float   then puts "a decimal number"
when String  then puts "some text"
end

B
a decimal number

then lets you keep a short branch on one line. 80...90 (three dots) means 80 up to but not including 90 — the Ranges lesson explains the difference between .. and ....

Ruby 3 also has a more powerful case ... in form for pattern matching on arrays and hashes, covered in Level 2.

Common mistakes

• Forgetting the else branch, so an unexpected value silently produces nil.

Practice

Given a month number from 1 to 12, print the season (Northern Hemisphere): 12, 1, 2 → winter; 3–5 → spring; 6–8 → summer; 9–11 → autumn.

month = 7

season = case month
         when 12, 1, 2 then "winter"
         when 3..5 then "spring"
         when 6..8 then "summer"
         when 9..11 then "autumn"
         else "invalid month"
         end

puts season

summer