Private method called error

Question

Have written a method; when I try to run it, I get the error:

NoMethodError: private method ‘subtotal’ called for 39.99:Float
at top level    in grades.rb at line 9
Program exited with code #1 after 0.04 seconds.

Following is the code:

def subtotal(qty = 1)
  return nil if self.to_f <= 0 || qty.to_f <= 0
  self.to_f * qty.to_f
end

book = 39.99
car = 16789

puts book.subtotal(3)
puts car.subtotal
puts car.subtotal(7)

Answer 1

When you declare a method outside of any class, it's a private method, which means it can't be called on other objects. You should open the class that you want the method to go into and then put the method definition in there. (If you want it in multiple classes, either open a common superclass or put it in a module and include that module in all the classes.)