title: Add to cart function in shopping app
body: <p>Here is my app how it look likes:</p>
  
  <p><a href="https://i.stack.imgur.com/ddzTJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ddzTJ.png" alt="add"></a></p>
  
  <p>when user clicked into the certain product:</p>
  
  <p><a href="https://i.stack.imgur.com/ypw5I.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ypw5I.png" alt="add2"></a></p>
  
  <p>Now what i wanted to do is, when user clicked add to cart, how should i save the product id and display later? is it i have to save the productid using NSUserDefaults? or is it any other way to do it?</p>