You need to pay attention to []
when you write code like this:
str = str[0..(length-5)] + str[(length-4)..length].upcase
If an index is negative, it is counted from the end of string. For example:
str = "abcde"
str[-1] # => "e"
str[-2] #=> "d"
See String.[] for more details.
With regard to your question, here is my logic:
break if str == "q"
if str.length < 4
str = str.upcase
else
str = str[0...-4] + str[-4..-1].upcase
end
p str