.rb

# Return the middle character of a string. Return the middle two characters if
# the word is of even length, e.g. middle_substring("middle") => "dd",
# middle_substring("mid") => "i"
def middle_substring(str)
  finalString = ""
  if (str.length % 2) == 0
     x = str.chars
     finalString += x[(x.(length/2).ceil]
     finalString += x[x.(length/2).floor]
  else
    x = str.chars
    finalString += x[x.(length/2).ceil]
  end
  return finalString
end