title: Undefined symbols for architecture x86_64 error on xcode
body: <p>I have a simple project, on my basic <code>ViewController.m</code> i'm trying to move to another <code>UIViewController</code> by doing:</p>
  
  <pre><code>@implementation ViewController
  
  - (void)viewDidLoad {
  [super viewDidLoad];
  ...
  }
  
  - (void)addAlarmBrick {
  NewAlarmViewController *navc = [[NewAlarmViewController alloc] init];
  [self presentViewController:navc animated:YES completion:nil];
  }
  </code></pre>
  
  <p>I have the NewAlarmViewController on my project with the <code>.m</code> file listed in the target membership.</p>
  
  <p>This is the full error message:</p>
  
  <pre><code>Undefined symbols for architecture x86_64:
  "_OBJC_CLASS_$_NewAlarmViewController", referenced from:
   objc-class-ref in ViewController.o ld: symbol(s) not found for architecture x86_64
   clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>what am i doing wrong over here?</p>
  
  <p><strong>EDIT:</strong></p>
  
  <p>Adding the settings for both files:</p>
  
  <p>.m file:</p>
  
  <p><img src="https://i.stack.imgur.com/PRaJU.png" alt=".m"></p>
  
  <p>.h file:</p>
  
  <p><img src="https://i.stack.imgur.com/BPigM.png" alt="enter image description here"></p>