From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2012-02-10T00:58:21+09:00
Subject: Re: why doesn't work

On Thu, Feb 9, 2012 at 4:17 PM, luk malcik <aport99@gmail.com> wrote:
> why method pierw doesn't run?
>
>
> class Wielomian
>   attr_accessor :a, :b, :c
>
>  def initialize
>   @d
>  end
>
>  def +(other)
>   result = Wielomian.new
>   result.a = self.a + other.a
>   result.b = self.b + other.b
>   result.c = self.c + other.c
>   result
>  end
>
>  def -(other)
>   result = Wielomian.new
>   result.a = self.a - other.a
>   result.b = self.b - other.b
>   result.c = self.c - other.c
>   result
>  end
>
> def *(other)
>   result = Wielomian.new
>   result.a = self.a * other.a
>   result.b = self.b * other.b
>   result.c = self.c * other.c
>   result
>  end
>
> def /(other)
>   result = Wielomian.new
>   result.a = self.a / other.a
>   result.b = self.b / other.b
>   result.c = self.c / other.c
>   result
>  end
>
>  def delta
>   @d = b**2 - (4*a*c)
>  end
>
> def pierw
>  x1 = -(b - (Math.sqrt(@d))/2*a)
>  end
>
> end

There are several strange things here. First of all, in initialize, @d
evaluates to nil and doesn't setup anything at all. You define
attr_accessor for a, b and c, so I guess the client code does:

w = Wielomian.new
w.a = 3
w.b = 4
w.c = 5

If you then call w.pierw, @d is still nil. You might be better off
(but we need more information) to assign a, b and c in the initialize
method, which right away could calculate the value for @d, setting
your object in a complete state:

class Wielomian
  def initialize a,b,c
    @a = a
    @b = b
    @c = c
    delta
  end

 # ... the rest
end

w = Wieloman(3,4,5)
w.pierw

Also, in the pierw method, assigning to a local variable x1 that is
not used is useless. You can drop the assignment.

Hope this helps,

Jesus.