NSMutableArray arrayWithCapacity问题

Question

I am deeply sorry as if this is a stupid question. if it is please leave a comment and I will remove it but here is my code below:

NumberedArray = [NSMutableArray arrayWithCapacity:50];
NSUInteger randomNumber = arc4random() % [NumberedArray count];
for (int i = 0; i<randomNumber; i++) {
    // Run some code
}

}

Now I get an error of: Thread 1: EXC_ARITHMETIC (code=EXC_I386_DIV, subcode=0X0)

So my best Guess is that the machine is getting confused because I am telling it that this array has capacity of 50 and now pick one of its slots randomly and perform some code is long as the loop is less than this randomly picked number.

but what I really want to do is to have the computer run a code based on randomly picked time interval.

This is a game where this code performs a enemy moving from left to right based on randomly picked time interval. Is this even a right approach? and if not what should I try instead? Thanks.

Answer 1

Capacity 50 doesn't mean your array contains 50 elements. Its count is 0. So you perform division by zero and that's why it crashes. Forget about using arrayWithCapacity: or initWithCapacity: because it doesn't mean anything practically helpful.

UPDATE:

If you need random number in a range of 50 then why not use just:

NSUInteger randomNumber = arc4random() % 50;

and initialise your array like this:

numberedArray = [NSMutableArray array];