title: Regular expression to match one of two characters
body: <p>What regular expression can I use to make sure input matches either a character 'a' or character 'x'.</p>
  
  <p>I have tried the following but this doesn't work as I had hoped.</p>
  
  <pre><code>char option;
  
  Console.WriteLine("Please make your option");
  for (int i = 0; i &lt; options.Length; i++)
  {
      Console.WriteLine(options[i]);
  
  }
  option = char.Parse(Console.ReadLine());
  while (option != 'a' || option != 'x')
  {
      Console.WriteLine("'a' or 'x' please!!");
      option = char.Parse(Console.ReadLine());
  }
  </code></pre>
  
  <p>What I want is for one of the two characters to be accepted only...as input.</p>