title: Semantic Issue: Use of undeclared identifier
body: <p>I am creating a game that has players swiping the planes into the correct lanes. However, I recently added a airplane to my game screen. However, Xcode says that I am using and undeclared identifier. I am new to this so please help.
  <br />
  Here is my header file controlling the game.
  GamePlayViewController.h</p>
  
  <pre><code>#import &lt;UIKit/UIKit.h&gt;
  
  @interface GamePlayViewController : UIViewController
  
  @end
  </code></pre>
  
  <p>Here is my GamePlayViewController.m This is where the error appears.</p>
  
  <pre><code>    #import "GamePlayViewController.h"
  
  #import "Airplane.h"
  
  @interface GamePlayViewController ()
  
  @end
  
  @implementation GamePlayViewController
  
  -(void) viewWillAppear:(BOOL)animated {
      //Add a vehicle
      Airplane* v = [[Airplane alloc]
                     initWithFrame:CGRectMake(221, 228, 0, 0)
                     [self.view addSubview:v];
  }
  
  @end
  </code></pre>
  
  <p>The error is at the Airplane* v [[Airplane alloc]. It says Use of undeclared identifier "Airplane" and also "v"</p>
  
  <p>I have searched all over Google and Stackoverflow for the answer, but none of the scenarios matched my situation. </p>
  
  <p>By the way, thanks in advance to whoever answers.</p>