elegant way to check if a string inputed by user is an integer in ruby?

Question

I'm trying to validate that the input a user gives my program via gets is an integer. is_a?(Integer) does not work, as far as i can tell, because gets gets a string from the user, so it will always return false even if the user enters an valid integer (in string form). One would think I could simply use to_i on the input and be done with it, but that raises another issue - "75akjfas".to_i results in 75. So if I relied on to_i to solve my problems, anything starting with numbers will work.

How do I cleanly validate that the value is an integer only, and not a combination of numbers and letters? Or do I need to resort to regex for this?

possible duplicate of Does ruby 1.9.2 have an is_a? function? — Andrew Grimm
– Andrew Grimm, Commented Jun 20, 2011 at 0:24

steenslag · Accepted Answer · 2011-06-19 23:44:47Z

7

print "Enter an integer (or try to sneak by something other): "
puts Integer(gets) rescue puts "Hey, that's not an integer!"

edited Jun 19, 2011 at 23:44

answered Jun 19, 2011 at 23:36

steenslag

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1 Comment

matt Over a year ago

I'd just add a quote from the docs: "strings should be strictly conformed to numeric representation. This behavior is different from that of String#to_i"

Roland Mai · Accepted Answer · 2011-06-19 23:28:03Z

6

How about s.to_i.to_s == s? I'd prefer regex however.

answered Jun 19, 2011 at 23:28

Roland Mai

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1 Comment

Tony Stark Over a year ago

i have no reason to not use regexp. i'm just hoping there's a nice helper function somewhere that i'm missing :).

siame · Accepted Answer · 2011-06-19 23:44:24Z

1

Using regex you could do it like this:

class String
  def integer?
   !!(self =~ /^[-+]?[0-9]+$/)
  end
end

answered Jun 19, 2011 at 23:44

siame

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Comments

Scott Bartell · Accepted Answer · 2016-07-11 01:30:47Z

1

You could use Integer() but you need to be careful with hex, binary, or octal input. http://ruby-doc.org/core-2.3.1/Kernel.html#method-i-Integer

def valid_integer?(string)
  begin
    !!Integer(string)
  rescue ArgumentError
    false
  end
end

answered Jul 11, 2016 at 1:30

Scott Bartell

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Comments

ogbeks · Accepted Answer · 2015-09-08 23:46:36Z

0

Check this code example for how to use the checked string input by the user
puts "Enter a number: " user_input = gets.chomp check = (user_input.to_i.to_s == user_input)

while (!check ) do
 puts("Wrong Input, Pls, Enter a number: " )
 user_input = gets.chomp
  check = (user_input.to_i.to_s == user_input)
end

if user_input.to_i < 0
puts "Number is negative"
elsif user_input.to_i > 0
puts "Number is positve"
else
puts "Number is Zero"
end

edited Sep 8, 2015 at 23:46

answered Sep 7, 2015 at 21:54

ogbeks

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2 Comments

J0e3gan Over a year ago

The link you have provided yields an application error. Maybe that is just a passing circumstance, but consider whether it is a lasting one you need to correct. Also, the connection between the link you have provided and the sample code in your answer is not very clear. Are they the same? Edit your answer to make it clear.

ogbeks Over a year ago

thanks @J0e3gan i have removed the link and it does show the same thing just that you can be able to run it there... I noticed the link was private to me.

queru · Accepted Answer · 2015-01-15 15:51:03Z

-2

Ruby can do it without esoteric solutions:

Integer is a integer

1970.is_a?Integer
true

String is not a integer

"1970".is_a?Integer
false

String to integer is a integer

"1970".to_i.is_a?Integer
true

answered Jan 15, 2015 at 15:51

queru

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2 Comments

oligofren Over a year ago

This seems not to be totally correct. @LyleDickie wrote this as a suggested edit: Unfortunately the "String to integer is a integer" section is incorrect. If you run it in IRB it does return true. However, if the user were to enter "197e" it would also evaluate to true. ``` "197e".to_i.is_a?Integer true ```

kgpdeveloper Over a year ago

"a".to_i is 0. Which is still an integer.

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