str_float_conversion.rb

# Change a sci-notation string to a float string without using the Numeric class in between. At all.

# Assume input string in "12345e7" format,
# return string in "123450000000.0" format
def exp2sf(exp_str)
  mant, ex = exp_str.split("e")

  zeroes = ""
  next_place_zeroes = "0"

  # From least-significant to most-significant
  ex.reverse.each_char do |ex_digit|
    this_place_zeroes = next_place_zeroes
    next_place_zeroes = next_place_zeroes + next_place_zeroes +
        next_place_zeroes + next_place_zeroes +
        next_place_zeroes + next_place_zeroes +
        next_place_zeroes + next_place_zeroes +
        next_place_zeroes + next_place_zeroes

    ("1"..ex_digit).each { zeroes += this_place_zeroes }
  end

  mant + zeroes + ".0"
end

puts exp2sf("123e5")
puts exp2sf("123e47")
puts exp2sf("123e47").length

puts exp2sf("123e421")
puts exp2sf("123e421").length