I'm trying to check if the string is a valid phone number in the format
"XXXX XXXX", where every X is an integer from 0 to 9. If its valid return TRUE, else return FALSE. 

I'm not sure why `!(0..9).include?(char)` doesnt work properly.

Any advice would be appreciated.
Thanks

```
def phone_number(str)
  if str.length == 9 && str[4] = " "
    str[4] = ""   
    str.each_char do |char|
      if !(0..9).include?(char)
        print false
      end
    end
    return true
  end
  return false
end

print phone_number("1234 5678") # => true
puts
print phone_number("123 5678") # => false
puts
print phone_number("1234 df78") # => false
puts
print phone_number("12345678") # => false

```