ios - Not visible @interface for 'MyController' declares the selector -

i'm learning ios development , found app source sample in internet. im trying rewrite , use tabbed layout, , after copying appdelegate.m sample app, got following error:

no visible @interface 'firstviewcontroller' declares selector alloc 

in following line:

firstviewcontroller *firstviewcontroller = [[firstviewcontroller alloc] initwithnibname:@"firstviewcontroller" bundle:nil]; 

this full appdelegate:

#import "appdelegate.h"      #import "firstviewcontroller.h"      @implementation appdelegate      - (bool)application:(uiapplication *)application didfinishlaunchingwithoptions:(nsdictionary *)launchoptions     {         self.window = [[uiwindow alloc] initwithframe:[[uiscreen mainscreen] bounds]];         // override point customization after application launch.          firstviewcontroller *firstviewcontroller = [[firstviewcontroller alloc] initwithnibname:@"firstviewcontroller" bundle:nil];         self.navigationcontroller = [[uinavigationcontroller alloc] initwithrootviewcontroller:firstviewcontroller];         self.navigationcontroller.navigationbar.barstyle = uibarstyleblackopaque;         self.window.rootviewcontroller = self.navigationcontroller;         [self.window makekeyandvisible];         return yes;     }      - (void)applicationwillresignactive:(uiapplication *)application     {         // sent when application move active inactive state. can occur types of temporary interruptions (such incoming phone call or sms message) or when user quits application , begins transition background state.         // use method pause ongoing tasks, disable timers, , throttle down opengl es frame rates. games should use method pause game.     }      - (void)applicationdidenterbackground:(uiapplication *)application     {         // use method release shared resources, save user data, invalidate timers, , store enough application state information restore application current state in case terminated later.         // if application supports background execution, method called instead of applicationwillterminate: when user quits.     }      - (void)applicationwillenterforeground:(uiapplication *)application     {         // called part of transition background inactive state; here can undo many of changes made on entering background.     }      - (void)applicationdidbecomeactive:(uiapplication *)application     {         // restart tasks paused (or not yet started) while application inactive. if application in background, optionally refresh user interface.     }      - (void)applicationwillterminate:(uiapplication *)application     {         // called when application terminate. save data if appropriate. see applicationdidenterbackground:.     }      @end 

same error (with selector inithwithnibname:bundle) in firstviewcontroller.m file

myviewcontroller* mycontroller  = [[myviewcontroller alloc] initwithnibname:@"myviewcontroller" bundle:nil]; 

i don't know error means after googling it, , can't how fix it. in advance!

you should use different names variables , classes.

change:

firstviewcontroller *firstviewcontroller = [[firstviewcontroller alloc] initwithnibname:@"firstviewcontroller" bundle:nil]; 

to:

firstviewcontroller *firstviewcontroller = [[firstviewcontroller alloc] initwithnibname:@"firstviewcontroller" bundle:nil];