.upcase! makes if statement fail to work properly

Question

begin
puts "Enter selection:\n\n"
$main = gets.chomp

        if $main.upcase! == "A"
                    call_function_1
        elsif $main.upcase! == "B"
                    call_function_2
        end

end while $main != "~"

With the code as it is, entering A runs call_function_1, but entering B seems to be ignored.

The issue appears to be the .upcase! , as when I remove it, it works fine... why?

http://www.tutorialspoint.com/ruby/ruby_if_else.htm Pretty sure, i could be wrong. You need the else in your if statement. — Duck1337, Jul 17 '14 at 21:08
Your code is fine, if you didn't mess up with the indentation. — theharshest, Jul 17 '14 at 21:12
If I enter B at the prompt, it ignores the input and does not call call_function_2. If I then swap the two, it will ignore A and not call call_function_1. — Will Von Wizzlepig, Jul 17 '14 at 21:21
OK. I tried the code all by itself, and it works fine there. I must have something crazy going on in my main program. I thought I was up against some limitation of a while loop, but it's most likely my newbie code. Thank you for the help! — Will Von Wizzlepig, Jul 17 '14 at 21:26
Crud. It was $main.upcase! (which I left out of the example)... when I removed the .upcase!, it all works fine now. — Will Von Wizzlepig, Jul 17 '14 at 21:37

sawa · Answer 1 · 2014-07-18T08:25:06.017

I don't understand your code particularly, but you may be having a common beginner's mistake to use destructive methods when you shouldn't. upcase! will return nil when no upcase takes place, and that may be causing your problem. Especially, you are doing upcase! on a string $main, and then doing upcase! on it again. If there were no upcasing in the first upcase!, then you would be calling the second upcase! on nil, which will raise an error. Even if there were upcasing in the first upcase!, the second upcasing will surely not take place, and you will get nil even in that case. It does not makes sense at all. Change upcase! to upcase.

By the way, I don't understand why you are using chomp correctly (instead of chomp!), but are using upcase! (instead of upcase). And I also don't understand why you are using the former chained after gets (which is okay) but are doing the latter within each condition in if elsif end block (which is not only redundant, but problematic).

Furthermore, it looks like you should be using case end instead.

when I first wrote it, it said something like "unrecognized variable 'upcase'", but when I added ! then it worked. I am very new to programming so it is likely I am doing MANY things the wrong way, but thank your for the help. 私はまだ未熟者プログラマーだから、助けてくれましたありがとうございます。 — Will Von Wizzlepig, Jul 18 '14 at 15:14

score 0 · Accepted Answer · answered Jul 18 '14 at 00:14

You should be using upcase, not upcase!. I would also use a case statement instead of the if block.

begin
  puts "Enter selection:\n\n"

  input = gets.chomp

  case input.upcase
  when 'A'
    call_function_1
  when 'B'
    call_function_2
  end

end while $main != "~"

.upcase! makes if statement fail to work properly

2 Answers2