Question

I just try to solve problem #45 from project-euler using ruby. I know the approach. But I wrote the code, It doesn’t run. I am new to ruby, I don’t know why there has to be so many “end” keyword at the back(Or else the terminal will complain)

Here is the code:

class Test
    def initialize()

    end

    def Triangle(n)
        if 1 + 8*n < 0 then
            return false
        else
            i1 = 0.5 * (-1 + Math.sqrt(1 + 8*n))
            i2 = 0.5 * (-1 - Math.sqrt(1 + 8*n))
            cut_i1 = i1.to_i
            cut_i2 = i2.to_i
            if (cut_i1 == i1) & (i1 > 0)
                return true
            else if (cut_i2 == i1) & (i2 > 0)
                return true
            else
                return false
            end
        end
    end

    def Pentagonal(n)
        delta = 1 + 24*n
        if delta < 0 then
            return false
        else
            r1 = (1.0/6) * (1 + Math.sqrt(delta))
            r2 = (1.0/6) * (1 - Math.sqrt(delta))
            cut_r1 = r1.to_i
            cut_r2 = r2.to_i
            if (cut_r1 == r1) & (r1 > 0)
                return true
            else if (cut_r2 == r1) & (r2 > 0)
                return true
            else
                return false
            end
        end
    end 

    def Hexagonal(n)
        delta = 1 + 8*n
        if delta < 0 then
            return false
        else
            r1 = 0.25 * (1 + Math.sqrt(delta))
            r2 = 0.25 * (1 - Math.sqrt(delta))
            cut_r1 = r1.to_i
            cut_r2 = r2.to_i
            if (cut_r1 == r1) & (r1 > 0)
                return true
            else if (cut_r2 == r1) & (r2 > 0)
                return true
            else
                return false
            end
        end
    end
end
for i in (1...100)
    o = Test.new
    print o.Triangle(i)
end

end
end
end

What’s happening. Every time I run the program from the terminal. It shows nothing….

Answer 1

It’s because you are using else if instead of elsif. Compare:

if cond
  # do something
elsif another_cond
  # do something else
end


if cond
  # do something
else
  if another_cond
    # do something else
  end
end

With that in mind, your program does not do what you think it should. Fix the elsif‘s and see.