title: How to multiply every other element of an array?
body: <p>Let's say that I have an array like this:</p>
  
  <pre><code>[1,2,3,4,5,6,7]
  </code></pre>
  
  <p>how can I multiply every other number of this array except the first by 2
  so my new array looks like this</p>
  
  <pre><code>[1,4,3,8,5,12,7]
  </code></pre>