Why do i get an error comparing NSString's? (-[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance)

I have a `NSMutableArray (_theListOfAllQuestions)` that I am populating with numbers from a file. Then I compared the objects in that array with `qNr (NSString)` and I got error. I even casted the array to another `NSString`, `_checkQuestions`, just to be sure I am comparing `NSStrings`. I tested using item to compare also. ``` -(void)read_A_Question:(NSString *)qNr { NSLog(@"read_A_Question: %@", qNr); int counter = 0; for (NSString *item in _theListOfAllQuestions) { NSLog(@"item: %@", item); _checkQuestions = _theListOfAllQuestions[counter]; //_checkQuestion = NSString NSLog(@"_checkQuestions: %@", _checkQuestions); if ([_checkQuestions isEqualToString:qNr]) { NSLog(@">>HIT<<"); exit(0); //Just for the testing } counter++; } ``` When running this code i get the following `NSLog`: ``` read_A_Question: 421 item: 1193 _checkQuestions: 1193 ``` ...and error: -[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance 0x9246d80 *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFNumber isEqualToString:]: unrecognized selector sent to instance 0x9246d80' I do believe that I still comparing `NSString` with a number of some sort but to me it looks like I am comparing `NSString` vs. `NSString`? I could really need some help here to 1) understand the problem, 2)solve the problem?