title: Checking if a specified position in a string contains a letter or a digit
body: <p>I wish to check whether a string contains a letter or a digit in a specified position.</p>
  
  <p>Here's the problem:</p>
  
  <p>I have a input string of length 2. The string is of the form <em>"a1"</em>. 
  I'm making a validation method for these types of strings.</p>
  
  <p>Requirements:</p>
  
  <ul>
  <li>the letter at index position 0 has to be one of the letters: a, b, c, d, e, f, g, h</li>
  <li>the number/digit at index position 1 has to be one of the numbers: 1, 2, 3, 4, 5, 6, 7, 8</li>
  </ul>
  
  <p>Thanks!</p>