Exception Handling Help Xcode 4.6 - objective-c

Question

Hello I am pretty new to programming but I have been following a few tutorials in Objective C. I just came across a problem in a Exception Handling tutorial and well, my code didn't work the same way.
First of all this is my code in main:
#import < Foundation/Foundation.h>
#import "Numz.h"
int main(int argc, const char * argv[]){
#autoreleasepool {
Numz *n = [[Numz alloc]init];
#try {
[n thisisgoingtogetanerror] <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< error on this line
}
#catch (NSException *e) {
NSLog(#"you got an error in your program");
}
NSLog(#"this is code aftr the error");
}
return 0;
}
The error above says
no visible #interface for 'Numz' declares the selector
'thisisgoingtogetanerror'
My interface and implementation are created but have no variables or methods created inside, but isn't that why I need to handle the error in the first place?
Also, I can't get any kind of console view either, the build just fails and points me at that error.
It might be some settings in xcode 4.6 that I need to change but I can't get the code to run and handle the error. I have looked online and can't find any answers.
Any help would be great.

Answer 1

The compiler is complaining because you are calling a method that it has not seen a declaration of ever.
Change it to (assuming Numz is not a subclass of NSArray nor implements the count method): [n count];.
Note that you should never use exceptions for flow control. That is, you should not #throw an exception and then use #catch to process the exception and continue execution. Exceptions in iOS/Cocoa are only used to indicate unrecoverable errors.
Try this:
#interface NSObject(Badness)
- (void)methodBadness;
#end
Then call that method in your code. Compiler shouldn't warn, runtime should #throw.

Answer 2

Exception handling is used for errors/exceptions at runtime. But the error you get occurs at compile time
You can cause a runtime error through something like this:
#interface RuntimeError : NSObject
+ (void)cause;
#end
#implementation RuntimeError
+ (void)cause {
NSAssert(NO, #"This is a runtime error caused through a assertion failure")
}
#end
// Call it with
// [RuntimeError cause]
// inside the #try-Block