Calculation in a block

Ruby
1

Hi,

I’m new to ruby, and I am trying to add all the natural numbers below
one thousand that are multiples of 3 or 5. (exercise from ProjectEuler)

Here’s my code:

class Array
def sumNumbers
sum = 0
self.each_with_index { |n, i|
if ((self[i] % 3) == 0 || (self[i] % 5) == 0)
sum += self[i]
end
}
sum
end
end

numbers = [1…1000]
print "Sum of natural numbers till 1000 that are multiples of 3 or 5 is
" + numbers.sumNumbers

When I try to execute this, I get this error:

SumOfMults.rb:5:in block in sumNumbers': undefined method%’ for
1…1000:Range
(NoMethodError)
from SumOfMults.rb:4:in each' from SumOfMults.rb:4:ineach_with_index’
from SumOfMults.rb:4:in sumNumbers' from SumOfMults.rb:14:in’

Not sure how self[i] is actually treated as a Range. Can you please let
me know what’s wrong in my code?

Thanks,
Mouli

2

numbers = [1…1000]

In your code, numbers is an array with a single element. That single
element is a range of numbers from 1…1000. Instead, don’t you want
numbers to be an array like [1, 2, 3, 4, 5, …, 999, 1000]? You can
create this array by

numbers = Array.new(1000) { |i| i+1 }

–Alex

3

Alex DeCaria wrote:

numbers = [1…1000]

In your code, numbers is an array with a single element. That single
element is a range of numbers from 1…1000. Instead, don’t you want
numbers to be an array like [1, 2, 3, 4, 5, …, 999, 1000]? You can
create this array by

numbers = Array.new(1000) { |i| i+1 }

or:

numbers = (1…1000).to_a

4

On Tue, May 4, 2010 at 12:59 PM, Chandramouli Parasuraman
[email protected] wrote:
I would be more rubymatic here :wink:
1000.times.inject{ | sum_so_far, next_number |
if (next_number % 3).zero? || (next_number % 5).zero?
sum_so_far + next_number
else
sum_so_far
end
}

It might be exaggerated to use the implicit form of inject just
because the first value is zero (it will be passed to sum_so_far in
the first iteration)

inject(0){ | sum_so_far, next_number |
}
might have been more readable

HTH
R.

5

On Tue, May 4, 2010 at 1:37 PM, Brian C. [email protected]
wrote:

numbers = (1…1000).to_a

or even [*1…1000] ( remark that 1000 must not be in the solution here
).
However I feel it is completely inadequate to the solution to create
an array of 999 numbers.

R.

6

(1…1000).select{|n| n % 3 == 0 or n % 5 == 0}.inject{|sum,n| sum + n }

7

Great, now I understand. Works fine now with both Array.new(1000) {|i|
i+1} and the inject.

Thanks everyone.