title: PHP Switching between two variables equally without using database
body: <p>i need to switch between two variables so i am able to serve two variables equally</p>
  
  <p>for example i have </p>
  
  <pre><code>$ad1
  $ad2
  </code></pre>
  
  <p>i want to serve both ads equally using a light method with no database</p>
  
  <p>using random method won't serve both equally</p>
  
  <p>can you please guide me how to achieve this ?</p>