Re: newbie question

On 08/01/2011 12:50 PM, Chris White wrote:
>> class Factorial
>> def fact(n)
>> if n == 0
>>    1
>> else
>>    n * fact(n-1)
>> end
>> end
>> end
>>
>> my_fact = Factorial.new
>> puts "enter a positive integer: "
>> my_fact = gets.to_i
>> puts "factorial: #{fact(n)}"
>>
>> I get this error:
>>
>> marcc$ ruby factorial7.rb
>> enter a positive integer: 4
>> factorial7.rb:14:in `<main>': undefined local variable or method `n' for
>> main:Object (NameError)
>>
> There's two issues here. The first is that you renamed `n` to `my_fact`, so it becomes undeclared as the error mentions. The other is that since fact is now part of the Factorial class, you need to change how fact() is called:
>
> puts "factorial: #{my_fact.fact(n)}"
>
> More interesting stuff to help you along the learning path. Right now in order to access your fact function, you have to create a new instance of the class. Instead you can utilize what is known as a singleton method. So the class can be rewritten as such:
>
> class Factorial
>    def Factorial.fact(n)
>      if n == 0
>        1
>      else
>        n * fact(n-1)
>      end
>    end
> end
>
> puts Factorial.fact(10)
<snip>

Interesting. I usually see this written as

class Factorial
   def self.fact(n)
...

(or using class << self)

Also, it seems more natural to have Factorial be a module instead of a 
class, but that's not something the OP needs to worry about at this point.

-Justin