Need help validating if user input is a number

Question

I have the following code:

def say(msg)
  puts "=> #{msg}"
end

def do_math(num1, num2, operation)
  case operation
    when '+'
      num1.to_i + num2.to_i
    when '-'
      num1.to_i - num2.to_i
    when '*'
      num1.to_i * num2.to_i
    when '/'
      num1.to_f / num2.to_f
    end
end

say "Welcome to my calculator!"

run_calculator = 'yes'

while run_calculator == 'yes'
  say "What's the first number?"

  num1 = gets.chomp

  say "What's the second number?"

  num2 = gets.chomp

  say "What would you like to do?"

  say "Enter '+' for Addition, '-' for Subtraction, '*' for Multiplication, or '/' for Division"

  operation = gets.chomp

  if num2.to_f == 0 && operation == '/'
    say "You cannot devide by 0, please enter another value!"
    num2 = gets.chomp
  else
    result = do_math(num1, num2, operation)
  end

  say "#{num1} #{operation} #{num2} = #{result}"

  say "Would you like to do another calculation? Yes / No?"
  run_calculator = gets.chomp

  if run_calculator.downcase == 'no'
    say "Thanks for using my calculator!"
  elsif run_calculator.downcase == 'yes'
    run_calculator = 'yes'
  else
    until run_calculator.downcase == 'yes' || run_calculator.downcase == 'no'
      say "Please enter yes or no!"
      run_calculator = gets.chomp
    end
  end
end

I need it to take the num1 and num2 variables that the user inputs and validate that they are numbers and return a message if they aren't.

I would like to use a Regex, but I don't know if I should create a method for this or just wrap it in a loop.

When supplying code, reduce it to the bare minimum needed to replicate the problem. In other words, something like num1 = gets.chomp would be sufficient, along with another line showing how you tried to test for a numeric. — the Tin Man
– the Tin Man, Commented Nov 10, 2014 at 21:08

August · Accepted Answer · 2014-11-11 17:28:49Z

4

The Integer method will raise an exception when the given string is not a valid number, whereas to_i will fail silently (which I think is not desired behavior):

begin
  num = Integer gets.chomp
rescue ArgumentError
  say "Invalid number!"
end

If you want a regex solution, this will also work (although I recommend the method above):

num = gets.chomp
unless num =~ /^\d+$/
  say "Invalid number!"
end

edited Nov 11, 2014 at 17:28

answered Nov 10, 2014 at 20:55

August

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Comments

Cary Swoveland · Accepted Answer · 2014-11-10 23:28:33Z

0

You would often see each section written something like this:

ERR_MSG = "You must enter a non-negative integer"

def enter_non_negative_integer(instruction, error_msg)
  loop do
    puts instruction
    str = gets.strip
    return str.to_i if str =~ /^\d+$/
    puts error_msg
  end
end

x1 = enter_non_negative_integer("What's the first number?", ERR_MSG)
x2 = enter_non_negative_integer("What's the second number?", ERR_MSG)

Here's possible dialog:

What's the first number?
: cat
You must enter a non-negative integer
What's the first number?
: 4cat
You must enter a non-negative integer
What's the first number?
:             22
#=> 22
What's the second number?
: 51
#=> 51

x1 #=> 22
x2 #=> 51

answered Nov 10, 2014 at 23:28

Cary Swoveland

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