title: The type or namespace IHttpActionResult not found
body: <p>This is the first time I am creating a Web API application in ASP.NET MVC4. I opened a new Web API project and added a new controller named 'Product'. The function given below shows an error namespace not found. </p>
  
  <pre><code>public IHttpActionResult GetProduct(int id) 
  {
      var product = products.FirstOrDefault((p) =&gt; p.Id == id);
      if (product == null)
      {
          return NotFound();
      }
      return Ok(product);
   }
  </code></pre>
  
  <p>Can anyone help me to solve this problem?</p>