yangsu

4 + 4       # g8
4 + "foo"   # results in a TypeError, hence strongly typed
4 + 4.0     # => 8.0      this works because of type coercion

# What about this though?
def add_stuff
  4 + "foo"
end # => nil

add_stuff # => TypeError    This proves that Ruby is dynamically typed

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i = 0
a = ['100', 100.0, '50', 50.0]
while i < a.size
  <b>puts a[i].to_i</b>
  i = i + 1
end

yangsu

foo = 'hello, plcourse' # here we define a function. Notice there's no type declaration
foo = 'is mutable'      # variables are mutable, i.e. they can vary
CONSTANTS = 'are defined like this' # they are immutable

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puts(foo) # this prints "hello, plcourse" and returns nil
puts foo  # this is exactly the same as above, with a bit of syntactic sugar

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def be_truthful
  42
  true    # The last expression is always the one that gets returned
end

yangsu

foo = false or true    # This expression evaluates to true
# => true
foo                    # But it assigned foo to false
# => false

yangsu

[1, "two", 3] # is perfectly valid
Array.new     # remember, these are objects, and objects can be instantiated
              #   with .new()

cars = ['ford', 'toyota', 'subaru']
cars[0]     # => "ford"
cars[2]     # => "subaru"
cars[-1]    # => "subaru"
cars[-4]    # => nil
cars[9001]  # => nil

yangsu

# Literal Form
numbers = { 1 => 'one', 2 => 'two' }
# => {1=>"one", 2=>"two"}

# Accessing element using key
numbers[1] # => "one"

# Can use symbols as keys
stuff = { :array => [1, 2, 3], :string => 'Hello' }
# => {:array=>[1, 2, 3], :string=>"Hello"}

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def tell_the_truth(options={})
  if options[:profession] == :lawyer
    'it could be believed that this is almost certainly not false.'
  else
    true
  end
end

tell_the_truth
# => true

yangsu

class Fixnum
  def my_times
    i = self
    while i > 0
      i -= 1
      yield
    end
  end
end