From: Peter Vandenabeele <peter@...>
Date: 2011-09-24T17:52:10+09:00
Subject: Re: Conditional statements with multiple arguments

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On Sat, Sep 24, 2011 at 4:53 AM, Thomas B. <sinixlol@gmail.com> wrote:

> Good afternoon everyone,
>
> I'm a beginner in Ruby with a little bit of experience programming in
> Java and PHP. Right now I'm having a difficult time grasping conditional
> (if/elsif) statements in Ruby. I'm trying to get an if statement to
> evaluate two different strings...i.e.
>
> action = gets.chomp()
>
> if action == "M" || "m"
>  menu()
> else
>  puts "Please enter in a valid selection."
> end
>
> So, from what I'm used to in programming, the if action == "M" || "m""
> should evaluate to a conditional statement as to whether or not action
> is equal to the strings "M" or "m". However, this does not seem to be
> the case. It's not giving any kind of an error, however, it is calling
> the menu() method regardless of what is entered. I can easily make this
> work by separating the "M" and the "m" into an if and an elsif argument
> i.e:
>
> action = gets.chomp()
>
> if action == "M"
>  menu()
>
> elsif action == "m"
>  menu()
>
> else
>  puts "Please enter in a valid selection."
> end
>
> The above process does seem to work, however, isn't there a simpler way
> of accomplishing this so I'm not adding unnecessary conditional
> statements?


I believe a nice way to achieve it could be the "case" statement.
That does allow you to give a list of strings to match against.

E.g.

peterv@ASUS:~$ cat case.rb
action = gets.chomp()

case action
when "M", "m"
  puts "Found 'M' or 'm'"
else
  puts "Enter a valid selection"
end
peterv@ASUS:~$ ruby case.rb
A
Enter a valid selection
peterv@ASUS:~$ ruby case.rb
M
Found 'M' or 'm'
peterv@ASUS:~$ ruby case.rb
m
Found 'M' or 'm'
peterv@ASUS:~$

Of course, you could also have said:

if action.downcase == 'm'


> I've been trying to find more resources online about
> conditional statements with multiple arguments, but none of them have
> seemed to help out. I'm guessing that my understanding of the || and
> "or" statements is misguided.
>

The specific error in your original code

your code =>  if action == "M" || "m"

is that this will be interpreted as

  if (action == "M") || "m"

and that a string "m" evaluates to true. So what you where saying is:

   if (action is "M") or true

which will be always true.

HTH,

Peter

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