Re: How to inhibit the use of letters and allowing just numbers

Matt Victorio wrote in post #983494:
> Hello,
>
> I started using Ruby few weeks ago and I have a little problem:
>
> How do I inhibit the user of using numbers instead of letters?
>
> For exemple, I created a program that asks the user his age, but I want
> the user answer it using only numbers, not letters ('10', not 'ten').
> Which command do I use for returning the line 'use just numbers', for
> exemple?
>
> Please, tell me anything, even if it looks 'hard' :P

Please, always show your existing code, otherwise we are left guessing 
what you're doing.

My guess is that you're doing something like this:

  line = $stdin.gets
  age = line.to_i

Here, 'line' is always going to be a string of characters - if the user 
types 10 and hits Enter, you will get "1" "0" "\n".

You have several ways to enforce integerness. Here is one:

  line = $stdin.gets
  age = Integer(line)

That raises an exception if line consists of other characters (trailing 
spaces permitted). You could then rescue the exception. Note that it 
also interpets numbers beginning with '0' and '0x' as octal and hex 
respectively.

Probably a better solution is to match against a regular expression, so 
you can define exactly what is or is not acceptable input.

puts "How old are you?"
while line = $stdin.gets
  if line =~ /\A\d+\s*\z/
    age = line.to_i
    break
  else
    puts "Please enter a number!"
  end
end
puts "Next year you will be #{age+1}"

Notes:
\A = only match at start of string
\d = match digit [0-9]
\d+ = match 1 or more digits
\s = match space
\s* = match 0 or more spaces
\z = only match at end of string

(There is a bug if the user terminates the session without entering any 
age. I'll leave that to you to fix!)

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