From: "Jan E." <lists@...>
Date: 2012-10-17T03:35:22+09:00
Subject: Re: Converting binary string to integer for a Ruby newbie

Hi,

if you don't want to use the built-in methods, you'll have to loop over 
the characters and sum the values of the digits.

The easiest way is to start from right and let an index count from 0 up. 
This will give you the exponent of each power of 2:

num = '011001'
value = 0
'011001'.reverse.each_char.with_index do |dig, i|
  value += 2**i if dig == '1'
end
puts value

So for every digit "1", you add the corresponding value.

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