title: If statement to check whether a string has a capital letter, a lower case letter and a number
body: <p>Can someone give an idea on how to test a string that:</p>
  
  <ul>
  <li>contains at least one upper case letter</li>
  <li>contains at least one lower case letter</li>
  <li>contains at least one number</li>
  <li>has a minimal length of 7 characters</li>
  </ul>