Errors in trying to cast to NSInteger * and NSMutableArray * - objective-c

Question

I'm a newbie in obj c. So I have a simple question.
I have a matrix of NSInteger values. It is called "curBoard". I want to update value at (x,y) coordinates with value "curStep". I have an arror "operand of type void where arithmetic..."
What am I doing wrong ?
[curBoard replaceObjectAtIndex:x withObject:(NSMutableArray *)[[curBoard objectAtIndex:x] replaceObjectAtIndex:y withObject:(NSInteger *)[NSNumber numberWithInt:curStep]]];
Update:
NSMutableArray *board;
board = [NSMutableArray new];
for(NSInteger i = 0; i<boardSize; i++) {
NSMutableArray *row = [NSMutableArray new];
for(NSInteger j = 0; j < boardSize; j++)
[row addObject:(NSInteger *)[NSNumber numberWithInt:0]];
[board addObject:row];
}

Answer 1

This withObject:(NSInteger *)[NSNumber numberWithInt:curStep]] part is what causing an issue. If you are storing as NSNumber objects, you should just use:
... withObject:[NSNumber numberWithInt:curStep]]
Edit:
From the code posted above, you should add it as:
[row addObject:[NSNumber numberWithInt:0]];
NSInteger is not of pointer type and you should use NSNumber itself to add to array.

Answer 2

Objective-C is basically just a bunch of object syntax strapped to C. The overall effect is something like strapping a jetpack to a horse: sometimes the two parts don't really work together very well. In this case, you're trying to go faster by telling the horse to giddy up, when you should really be opening up the throttle.
NSMutableArray is part of the jetpack—it's an Objective-C object and is only equipped to handle arrays of Objective-C objects. But NSInteger is part of the horse—it's a primitive C integer type, not a real object.*
I know NSInteger is capitalized like a class and has an NS prefix like a class, but it's really a creature of C. You can confirm this yourself—type Cmd-O in Xcode and type "NSInteger" into the Open Quickly dialog that pops up, and you'll be able to jump to its definition. In my current Mac project, that's typedef long NSInteger;; long is one of the primitive C types.
NSNumber exists to bridge the two. It's an object specifically designed to hold the C numeric types inside it. Since NSNumber is an object, NSMutableArray and other Objective-C things can deal with it.
But you can't just cast between NSNumber and NSInteger. NSNumber holds an NSInteger inside it, but that doesn't mean it's actually an NSInteger itself. If you put a sandwich in a plastic bag, you can't eat the bag.
Instead, you have to use NSNumber's +numberWithInteger: method to construct an NSNumber, and -integerValue to get the integer back out of it. (+numberWithInt: and -intValue will usually work, but they may behave differently with very large values, depending on whether your app is running on a 32-bit or 64-bit processor.) Actually, nowadays you can say [NSNumber numberWithInteger:foo] as #(foo) instead, which is a lot shorter.**
So when you add a number, you should be saying:
[row addObject:#(0)];
And when you later want that number back, you'll want to say something like:
n = [[row objectAtIndex:y] integerValue];
The -replaceObjectAtIndex:withObject: error is a different story. -replaceObjectAtIndex:withObject: doesn't return anything at all, so you can't use it as an argument. Luckily, you don't need to in this case. -replaceObjectAtIndex:withObject: doesn't create a new array; it alters the array that's already inside [curBoard objectAtIndex:x], so you don't need to do anything to curBoard. Instead, you can just write:
[[curBoard objectAtIndex:x] replaceObjectAtIndex:y withObject:#(curStep)];
* You actually used NSInteger *, which is slightly different. The * means "pointer to", so NSInteger * is a pointer to a primitive integer. This is sort of like NSNumber *, a pointer to an NSNumber object, so the compiler allows you to cast it.
Note that casting a pointer doesn't convert the data at the other end of the pointer; it just makes the compiler interpret the same data in a different way. If you actually tried to use the NSInteger * pointer to get data, you would either get garbage data or (for reasons too large to fit within this margin) crash.
In this case, though, once you've Jedi mind-tricked the compiler into thinking that value is a pointer to an NSInteger, you try to pass it to to -addObject:. -addObject: expects a pointer to an object, so the compiler balks at passing a pointer to an NSInteger instead.
** This syntax will work as long as you're using the iOS 6 SDK Xcode 4.4 or later, even if you actually run the app on an older iOS. It will also automatically use the right +numberWithWhatever: method for you, so you don't have to worry about picking the best one. When you're using a numeric literal like 0, the parentheses are optional, but they're required when you use a variable or constant. Of course, you can still do it the wordy way if you want, but there's little point nowadays.