Accept only numeric input

Question

I want to force user to enter only numeric value from console. Below is my piece of code that is supposed to do that.

puts \"Enter numeric value: \"
result =         


        

Answer 1

If you mean integer by "numeral", then:

puts "Enter numeric value: "
result = gets.chomp
case result
when /\D/, ""
  puts "Invalid input"
else
  puts "Valid input."
end

It also takes care of empty strings, which would be turned into 0 by to_i, which you probably do not want.

Answer 2

Try regular expressions, like this:

puts "Enter numeric value: "
result = gets

if result =~ /^-?[0-9]+$/
    puts "Valid input"
else
    puts "Invalid input."
end

The example above allows only digits [0..9]. If you want to read not only integers, you can allow a dot as well: ^-?[0-9]+$/. Read more about regexp in Ruby: http://ruby-doc.org/core-2.2.0/Regexp.html

Answer 3

to_i will convert any string to an integer, even if it shouldn't:

"asdf".to_i

which returns 0.

What you want to do is:

puts "Enter numeric value: "
result = gets.chomp

begin
  result = Integer(result)
  puts "Valid input"
rescue ArgumentError, TypeError
  puts "Invalid input."    
  # handle error, maybe call `exit`? 
end

Integer(some_nonnumeric_string) throws an exception if the string cannot be converted to an integer, whereas String#to_i gives 0 in those cases, which is why result.to_i.is_a? Numeric is always true.