title: How do I loop a request for user input until the user enters the correct info?
body: <p>I am a beginner who is trying to learn Ruby. I have learned some of the easier stuff so far, but I seem to be stuck in trying to combine a couple of things I've learned. </p>
  
  <p>What I am trying to do is to ask the user a question and tell them to enter either 1 or 2. A simple if statement would let me respond with one option if they enter 1, and another option if they enter 2. However, if they enter something entirely different like a different number, a string, etc., how can I prompt them to try again and have it loop back to the original question?</p>
  
  <p>What I have so far looks something like this. </p>
  
  <pre><code>prompt = "&gt; " 
  puts "Question asking for 1 or 2." 
  print prompt
  user_input = gets.chomp.to_i
  
  if user_input == 1    
     puts "One response." 
  elsif user_input == 2   
     puts "Second response." 
  else    
     puts "Please enter a 1 or a 2." 
  end
  </code></pre>
  
  <p>This is where I'm stuck. How do I make it go back to the "Question asking for 1 or 2." until the user enters a 1 or 2? I know it's probably a loop of some kind, but I can't seem to figure out which kind to use and how to incorporate asking for user input repeatedly (if necessary) until getting the desired input. Any help would be greatly appreciated. Thanks. </p>