Method not recognizing boolean value

Question

I have a method which take two arguments. A value (fixnum) and a boolean.

However, line 4 isn't returning "C" and is returning "D". It isn't recognizing the boolean value and I am unsure why?

def grade(num_books, reads_books)
  if num_books < 10 
    return "D"
  elsif num_books < 10 && reads_books == true
    return "C"
  elsif num_books.between?(10, 20)
    return "C"
  elsif num_books.between?(10,20) && reads_books == true
    return "B"
  elsif num_books > 20
    return "B"
  else
    return "A"
  end
end

grade(9, true)

What are the rules for calculating the grade? In particular, the "A" grade cannot be reached, because num_books is either below 10, or between 10 and 20, or above 20. There isn't another "else" that could be met. — Stefan
– Stefan, Commented Aug 10, 2017 at 9:23

Andrey Deineko · Accepted Answer · 2017-08-10 09:02:00Z

2

The order of clauses matters. The first one condition met wins. You might reorder clauses to make it robust enough:

def grade(num_books, reads_books)
  if num_books < 10 && reads_books == true
    return "C"
  elsif num_books.between?(10,20) && reads_books == true
    return "B"
  elsif num_books < 10 
    return "D"
  elsif num_books.between?(10, 20)
    return "C"
  elsif num_books > 20
    return "B"
  else
    return "A"
  end
end

grade(9, true)

or, a bit more rubyish:

def grade(num_books, reads_books)
  if reads_books
    case num_books
    when 0...10 then "C"
    when 10..20 then "B"
    else "A"
    end
  else
    case num_books
    when 0...10 then "D"
    when 10..20 then "C"
    else "B"
    end
  end
end

edited Aug 10, 2017 at 9:02

Andrey Deineko

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answered Aug 10, 2017 at 8:57

Aleksei Matiushkin

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5 Comments

Andrey Deineko Over a year ago

I think elsif num_books < 10 should go as a second condition clause. UPD: now I doubt it matters. UPD2: I again think it should go above the elsif num_books.between?(10,20) && reads_books == true as it looks more logical to me :D

Aleksei Matiushkin Over a year ago

The correct answer to your doubts is: elsif should be avoided in ruby :)

Andrey Deineko Over a year ago

Yes, in general of course it should be avoided :) Which for sure makes my above reflections pointless.

Stefan Over a year ago

The methods are not equivalent. The first one always returns "B" if num_books is above 20, whereas the second one returns "B" or "A" depending on reads_books in that case.

Stefan Over a year ago

In fact, the original method's else cannot be reached – "A" is never returned. So this is most likely another bug you have fixed ;-)

Andrey Deineko · Accepted Answer · 2017-08-10 08:57:12Z

1

It is returning "D" because it passes the condition if num_books < 10.

answered Aug 10, 2017 at 8:57

Andrey Deineko

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