title: Swift 3 2d array of Int
body: <p>It's actually a very simple question, but after an hour I can not solve my problem.</p>
  
  <p>I need to create a 2d array of Int.</p>
  
  <pre><code>var arr = [[Int]]()
  or
  var arr : [[Int]] = []
  </code></pre>
  
  <p>tried to change value :</p>
  
  <pre><code>arr[x][y] = 1
  </code></pre>
  
  <p>fatal error: Index out of range</p>
  
  <p>Should I use APPEND or I need specify the size of the array?</p>
  
  <p>I'm confused..</p>