How do I check if an object exists at a certain index of an NSMutableArray?

Question

For instance, how could I verify if there is an item at the index 3?

The objects in the NSArray are instantiated from the class "Animal."

Answer 1

Well, since NSMutableArray has to hold non-nil objects, as long as the array is big enough, you know there's something at index i:

if ([myArray count] > 3) {
    id myObj = [myArray objectAtIndex:3];
    ...
}

If you needed to check something elsek, like say make sure it didn't have a reference to the NSNull singleton, you could then check

if (myObj != [NSNull null]) ...

Answer 2

Since there can be no 'gaps' in a NSMutableArray's storage, if your index is less than [array count], you can be certain an object is present at that index.