title: If user enter not correct data app must repeats question
body: <p>everyone! I'm newbie in Golang and I've a problem.
  I've some code like this (just example):</p>
  
  <pre><code>fmt.Println("yes or no:")
  if _, err := fmt.Scan(&amp;str); err != nil {
      panic(err)
  }
  if str == "no" {
      fmt.Println("You have to enter yes.")
      //What do I need to write this?
  }
  </code></pre>
  
  <p>I wont it shows the question "yes or no" again til an user enters correct data or terminate proccess.</p>