Ruby reads .50 as .5 - ruby

Question

I have an Item class, and I initialized five variables. I am trying to match the output in my terminal to the value of the expected_summary. I am calling Item.summary in the following code:
class Item
attr_reader :name, :description, :manufacturer, :price, :summary
def initialize (name, manufacturer, price, description=nil, summary=nil)
#name = name
#manufacturer = manufacturer
#price = price
#description = description
if description
#summary = "Name: #{name}
Description: #{description}
Manufacturer: #{manufacturer}
Price: $#{price}"
else
#summary = "Name: #{name}
Manufacturer: #{manufacturer}
Price: $#{price}"
end
end
end
#expected_summary = %q(Name: Spy Notebook
#Manufacturer: Spys-R-Us
#Price: $10.50)
item = Item.new("Spy Notebook", "Spys-R-Us", 10.50)
puts item.summary
When I pass a number 10.50 as the price argument, it returns as 10.5. I cannot figure out why. Why does Ruby read 10.50 as 10.5? Is there a way to correct this?

Answer 1

The answer is in the string format operator which allows you to coerce the float into a string with 2 decimal places. This method will also work to do the rounding of 3 digit numbers, I didn't try it any further, but I'm fairly certain it will work. Here is your original code modified to showcase exactly how it would work.
class Item
attr_reader :name, :description, :manufacturer, :price, :summary
def initialize (name, manufacturer, price, description=nil, summary=nil)
#name = name
#manufacturer = manufacturer
#price = "%.2f" % price
#description = description
if description
#summary = "Name: #{name}
Description: #{description}
Manufacturer: #{manufacturer}
Price: $#{#price}"
else
#summary = "Name: #{name}
Manufacturer: #{manufacturer}
Price: $#{#price}"
end
end
def price
#price
end
end
EDIT: I didn't see #tadman's comment until after posting this, he beat me to the answer.

Answer 2

Maybe you can define your custom method to format the number as string with two decimals:
def two_decimals(number)
number = Float(number)
price_split = number.to_s.split('.')
price_split[1] = price_split.last + '0'*(2-price_split.last.size) if price_split.last.size < 2
price_split.join('.')
end
two_decimals(10.25) #=> "10.25"
two_decimals(10.2) #=> "10.20"
two_decimals(10) #=> "10.00"
Or something better...

Answer 3

The usual way of formatting numbers is:
'%.02f' % number
Where that is the printf-style notation for describing how you want something formatted. This is inherited from C and shows up in a lot of other languages:
'%f' % number # A floating-point number with default precision
'%.02f' % number # A floating-point number rounded to 2 places
Within Rails you also have helper methods like number_with_precision which can handle localization cases where the decimal separator is not a dot:
number_with_precision(number, precision: 2, locale: :fr)
# => 1,50