title: Getting Strange Error Running Objective C Code
body: <p>My project have no visible error but when i try to run it gives following error</p>
  
  <pre><code>Undefined symbols for architecture i386:
    "_OBJC_CLASS_$_ConcreteScreen", referenced from:
        objc-class-ref in ViewController.o
  ld: symbol(s) not found for architecture i386
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>I am using my ContactScreen class in ViewController.m</p>
  
  <p>i tried by @class ContactScree and #import <code>"ContactScreen.h"</code></p>
  
  <p>and in my ViewController i am using it as <code>[ContactScreen myMethod];</code>
  when i comment out this line it work fine but now it is giving compile time error :(
  yesterday it was wroking fine</p>
  
  <p>here is my code </p>
  
  <pre><code>#import "ViewController.h"
  
  
  #import "ConcreteScreen.h"
  @interface ViewController ()
  
  @end
  
  @implementation ViewController
  
  
  
  
  -(IBAction)btnContactPress:(id)sender{
     NSLog(@"Contact Screen");
  
      ConcreteScreen *coontact = [[ConcreteScreen alloc]init];
  
  }
  </code></pre>