# Variables, nil, Strings and Symbols — Ruby

Source: https://www.geekswithgeeks.com/en/ruby/f-basics

> Use variables, truthiness, strings, symbols and numbers correctly.

## The basics, the Ruby way

Ruby variables need no declarations: `count = 0`. Naming conveys scope: `local_variable`, `@instance_variable`, `@@class_variable` (rarely used), `$global` (avoid) and `CONSTANT`. **`nil`** represents "no value", and in conditions only **`nil` and `false` are falsy**; everything else, including `0`, `""` and `[]`, is truthy, which surprises developers coming from JavaScript or Python. **Strings** are mutable sequences of characters with interpolation in double quotes (`"Total: #{total}"`); single quotes are literal. Many projects add the magic comment `# frozen_string_literal: true` so string literals are immutable, and Ruby 3.4 can emit deprecation warnings when unannotated literals are mutated, preparing for frozen literals by default. **Symbols** (`:paid`, `:city`) are immutable, interned identifiers, ideal for hash keys and names, while strings are for text data. Numbers include arbitrary-precision **Integer**, **Float** and **BigDecimal** (from the bigdecimal gem) for money; integer division truncates (`7 / 2` is `3`), so use `7.fdiv(2)` or `7 / 2.0` when you need decimals.

## Truthiness, symbols and numbers

Only nil and false are falsy; 0 and empty strings are truthy.

```ruby
# frozen_string_literal: true

stock = 0
puts "0 is truthy in Ruby" if stock          # prints
puts "empty string is truthy" if ""         # prints

city = nil
puts city.nil?                                # true
label = city || "Unknown"                     # default when nil or false

status = :paid                                # symbol: an identifier
puts status == :paid                          # true
puts "paid".to_sym == :paid                   # true

puts 7 / 2                                    # 3 (integer division)
puts 7.fdiv(2)                                # 3.5
puts 2**100                                   # big integers just work

require "bigdecimal"
exact = BigDecimal("0.1") + BigDecimal("0.2")
puts exact.to_s("F")                         # 0.3 exactly

greeting = "Hello"
# greeting << " world"                        # FrozenError with frozen_string_literal
new_greeting = "#{greeting} world"            # build a new string instead
```

## Only nil and false are falsy

A check like `if count` is true even when count is 0. Write `if count.positive?` or `unless count.zero?` to express what you mean.

**Quiz:** Which values are falsy in Ruby?

- [ ] 0, "", nil and false
- [ ] Only false
- [x] Only nil and false
- [ ] nil, false and empty arrays

*Answer:* Only nil and false. Ruby treats every value except nil and false as true in conditions.