title: increase number in Class CSS automatically
body: <p>I want to make the following happen in:</p>
  <p>There is a for loop generating images of a list. I still want to be capable of styling indiviual images with CSS, so I need to generate a unique Class for each element of the list.</p>
  <p>Is there a way to generate a string like (&quot;a&quot;) plus the generated number so that the result is a1, a2, a3, a4...(a.id)?</p>
  <p>Lets say the list is 4 elements long.</p>
  <pre><code>&lt;li *ngFor=&quot;let chair of chairs&quot;&gt;  
      class=&quot;a + {{ chair.id }}&quot;
  &lt;/li&gt;
  </code></pre>