Conditionals: if, elsif, else

A conditional lets your program make a decision: run some code only when a condition is true.

Real-world analogy: "If it's raining, take an umbrella; otherwise, wear sunglasses."

Syntax

if condition
  # runs when condition is true
elsif other_condition
  # runs when the first was false and this one is true
else
  # runs when none of the above were true
end

Note the spelling: elsif, not else if or elif.

Example

temperature = 18

if temperature > 25
  puts "It's hot"
elsif temperature > 15
  puts "It's pleasant"
else
  puts "It's cold"
end

Expected output

It's pleasant

Ruby checks each condition from top to bottom and runs only the first branch that matches. 18 > 25 is false, 18 > 15 is true, so it prints "It's pleasant" and skips the rest.

if returns a value

Because everything in Ruby is an expression, you can assign the result of an if:

age = 20
status = if age >= 18
           "adult"
         else
           "minor"
         end
puts status

adult

For short choices like this, the ternary operator is common: status = age >= 18 ? "adult" : "minor".

Common mistakes

• Writing else if — Ruby treats that as a nested if that needs its own end, which usually ends in a syntax error.
• Putting conditions in the wrong order. if score > 50 before if score > 90 means the second branch can never run.

Practice

Write a program that stores an age and prints adult if it's 18 or over, teen if it's 13 to 17, and child otherwise.

age = 15

if age >= 18
  puts "adult"
elsif age >= 13
  puts "teen"
else
  puts "child"
end

teen