Ruby undefined method `+' for nil:NilClass

Question

I'm a total beginner in ruby but I can't get out of this issue I get these when I run the code, it all works well until the end:

INPUT TEXT: It all works well until

INPUT SUBTEXT: ll

TEXT: It all works well until SUBTEXT: ll

OUTPUT: 4 15

undefined method +' for nil:NilClass (repl):18:in initialize'

   puts "\nINPUT TEXT:"
    @text =  gets.chomp

puts "\nINPUT SUBTEXT:" 
    @subtext = gets.chomp

    puts "\nTEXT: " + @text
    puts "SUBTEXT: " + @subtext
    puts "\n"
    i = @text.index (@subtext)

    puts "OUTPUT:"

    while i != -1
            puts  i.to_s + ' '
            i = @text.index @subtext, i+1
    end

Answer 1

In Ruby, String#index doesn't return -1 when the substring is not found; it returns nil . Change your condition from while i != -1 to while i . (This works because, unlike some other languages, Ruby considers the value 0 to be true; only false and nil are false.)

Answer 2

Index return nil if substrings doesn't exist. So this should solve this issue

@text =  gets.chomp

puts "\nINPUT SUBTEXT:"
@subtext = gets.chomp

puts "\nTEXT: " + @text
puts "SUBTEXT: " + @subtext
puts "\n"
i = @text.index (@subtext)

puts "OUTPUT:"
while i
  puts  i.to_s + ' '
  i = @text.index @subtext, i+1
end