ios - Use of undeclared identifier 'alert' -

I get an error that says: the use of undisclosed identifiers 'warning'

  NSLert * warning = [NSLLert warningWhite passage text: @ "Why?" Default button: @ "OK"]; Can anyone tell me why I got this error?  
 UPDATED:  
   
 
 
 I think that means  
  UIAlertView * alert  
 
 not 
 
  NSAlert * warning // "NSAlert" does not exist in the cocoa API.  
 
 Your query from the compiler is that it says that type  NSAlert  is undefined. If the type is undefined, you may get another error about the variable which is not undefined, which is why it says that  alert  is undefined.