Question

I’m trying to write a small program that asks a user to input a number and the program will determine if it’s a valid number. The user can enter any kind of number (integer, float, scientific notation, etc.).

My question is what regular expression should be used to keep something like “7w” from being matched as a valid number? Also I would like the number 0 to exit the loop and end the program, but as it’s written now 0 is matching valid like any other number. Any insight please?

x = 1

while x != 0
  puts "Enter a string"
  num = gets

  if num.match(/\d+/)
    puts "Valid"
  else
    puts "invalid"
  end

  if num == 0
    puts "End of program"
    x = num
  end   
end

Answer 1

To start with, you are overcomplicating the loop, secondly, your regular expression needs to be a bit more explicit. Try something like this:

x = 1

while x != 0
  puts "Enter a string"
  num = gets.chomp
  if num == "0"
    puts "exiting with 0"
    exit 0
  elsif num.match(/^[0-9](\.[0-9])?$+/)
    puts "Valid"
  else
    puts "invalid"
  end
end

This expression will match any number that contains a digit or a decimal, and will fail to match anything containing letters. If the string entered is exactly 0, the script will exit with status 0.