Values and expressions

The idea

Ruby expressions produce values, including if expressions. Variables refer to objects, and method calls request behavior from those objects. Strings support interpolation inside double quotes, while arithmetic follows the operand types. Start by tracing one expression at a time and distinguishing the value it returns from any text it prints. The p method is useful when inspecting strings and collections.

Only nil and false are falsey in Ruby. Zero, an empty string, and an empty array are all truthy, so presence checks are not the same as emptiness checks. Use an explicit predicate such as empty? when the requirement concerns content. A branch can assign its selected result directly, reducing temporary state while keeping the condition and its meaning visible.

count = 0
label = if count
  "present"
else
  "missing"
end
puts label
puts "Count: #{count}"

present
Count: 0

Zero is truthy, so the first branch supplies the label. Interpolation constructs text without turning the original count binding into a string.