find all words ending in "ing" in ruby

def find_all_words_ending_in_ing
  words = ["bring", "finger", "drought", "singing", "bingo", "purposeful"]
  new_word = []
  # Your code goes here
  words.find_all do |word|
    if word.last(3) == "ing"
      new_word << word
    end
  end
  new_word
  #  expected return value is ["bring", "singing"]
end

The code needs to iterate through the items in the array and output the words ending with "ing"

I get this error:

undefined method `last' for "bring":String (NoMethodError)
      if word.last(3) == "ing"
              ^^^^

I would suggest you use #select and #end_with? instead.

["bring", "finger", "drought", "singing", "bingo", "purposeful"].select { |s| 
  s.end_with? "ing" 
}

When executing your code, we see the following error.

Traceback (most recent call last):
        8: from /usr/local/bin/irb:23:in `<main>'
        7: from /usr/local/bin/irb:23:in `load'
        6: from /var/lib/gems/2.5.0/gems/irb-1.2.0/exe/irb:11:in `<top (required)>'
        5: from (irb):31
        4: from (irb):23:in `find_all_words_ending_in_ing'
        3: from (irb):23:in `find_all'
        2: from (irb):23:in `each'
        1: from (irb):24:in `block in find_all_words_ending_in_ing'
NoMethodError (undefined method `last' for "bring":String)

If you look at the documentation for the String class, there is not a #last method, which is exactly what the error is telling you.

However, #end_with? will take a string and check if that string is a suffix of the string you're calling the method on.

To disregard any trailing whitespace in the strings in your array, you may wish to use #rstrip.

["bring", "finger", "drought", "singing", "bingo", "purposeful"].select { |s| 
  s.rstrip.end_with? "ing" 
}

And if you don't care about case, then you can either lowercase the string:

["bring", "WING", "finger", "drought", "singing", "bingo", "purposeful"].select { |s| 
  s.rstrip.downcase.end_with? "ing" 
}

Or use a regular expression:

["bring", "WING", "finger", "drought", "singing", "bingo", "purposeful"].select { |s| 
  s =~ /ing\s*\Z/i
}

Or using the otherwise mentioned #grep:

["bring", "WING", "finger", "drought", "singing", "bingo", "purposeful"].grep(/ing\s*\Z/i)

If you're not afraid of regular expressions, there's a great tool for this job called grep which works a lot like¹ the command-line tool of the same name:

words.grep(/ing\z/)

Here \z means "end of string" in Ruby regexp notation.

--

¹ It also does way more than match strings as it leverages the === operator, so it is even more handy than you might think!

String has no last() method but
String has end_with? method.

Example:

words.select do |word|
  word.end_with? "ing"
end