set variable in hbs template using ember.js

I have an array of data and I need to iterate over it in my hbs template:

  <th>
    
  </th>



  <th>
    
  </th>

How do I declare a variable and increase it to replace the hardcoded value?

I tried to wrap with but that did not worked:

  
    <th>
      
    </th>
  

I'm using ember 2.13.