binary_search.rb

def binary_search(ordered_array, search_value)

  lower_bound = 0
  upper_bound = ordered_array.length - 1

  while lower_bound <= upper_bound do

    midpoint = (lower_bound + upper_bound) / 2

    value_at_midpoint = ordered_array[midpoint]

    if search_value == value_at_midpoint
      return midpoint
    elsif search_value < value_at_midpoint
      upper_bound = midpoint - 1
    elsif search_value > value_at_midpoint
      lower_bound = midpoint + 1
    end

  end
  return nil
end