Format ruby variable to us dollar

string_to_dollars.rb

# use the .to_dollars method on any string and get appropriate
# dollar amount returned with two decimal places rounded to the hundreths
# format is for us dollar
class String
  def to_dollars
    d = self.decimals_present 
    return "$" + self + "00" if d == 0
    return "$" + self + "0" if d == 1
    return "$" + self if d == 2
    return "$" + self.decimals[1] + '.' + self.round_decimals if d > 2
  end
  def round_decimals
    d = self.decimals[0].split('')[0..1]
    d[0] + (d[1].to_i + 1).to_s
  end
  def decimals
    self.split('.').reverse
  end
  def decimals_present
    self.split('.').reverse[0].length
  end
end
float = 123.305                #=> 123.305
float.to_s.to_dollars          #=> "$123.31"
int = 123                      #=> 123
int.to_s.to_dollars            #=> "$123.00"
str = "123.30"                 #=> "123.30"
str.to_dollars                 #=> "$123.30"