to check app running first time or not on iphone

NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
if (![prefs objectForKey:@"alert"]) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"this is 1st time" message:@"Some description"
delegate:self cancelButtonTitle:@"Ok" otherButtonTitles:nil];
[alert show];
[alert release];
[[NSUserDefaults standardUserDefaults] setBool:YES forKey:@"alert"];
}
else {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:nil message:@" this is 2nd time!" delegate:self cancelButtonTitle:@"OK" otherButtonTitles:nil]; [alert show]; [alert release];
NSLog(@" DEJA VU");

}

[[NSUserDefaults standardUserDefaults] synchronize];