title: AngularJS how to add numbers inside the expression from a textbox?
body: <p>I have a problem adding a number from a textbox and place it on another textbox. My situation is like this:</p>
  
  <p>I have one textbox:</p>
  
  <pre><code>&lt;input type="text" ng-model="num1" /&gt;
  </code></pre>
  
  <p>And whatever the input is on this textbox, this will be the value of another textbox like this:</p>
  
  <pre><code>&lt;input type="text" value="{{ num1 + 1 }}" /&gt;
  </code></pre>
  
  <p>This setup shows successfully but with errors. When I type <code>2013</code> on the first, the second shows <code>20131</code> instead of <code>2014</code>.
  I also tried using filters like this:</p>
  
  <pre><code>&lt;input type="text" value="{{ num1 + 1 | number}}" /&gt;
  </code></pre>
  
  <p>but unfortunately, it doesn't work. What did I miss?</p>