-(void)addButtonClicked: will crash after delete all books

[nellace]

- (void)addButtonClicked:(id)sender {
    int a[6] = {1, 2, 5, 7, 9, 22};
    NSMutableIndexSet *indexSet = [NSMutableIndexSet indexSet];
    NSMutableArray *arr = [NSMutableArray array];
    NSMutableArray *stat = [NSMutableArray array];
    for (int i = 0; i < 6; i++) {
        [indexSet addIndex:a[i]];
        [arr addObject:[NSNumber numberWithInt:1]];
        [stat addObject:[NSNumber numberWithInt:BOOK_UNSELECTED]];
    }
    [_bookArray insertObjects:arr atIndexes:indexSet];
    [_bookStatus insertObjects:stat atIndexes:indexSet];
    [_bookShelfView insertBookViewsAtIndexs:indexSet animate:YES];

the random number in indexset is bound to beyond bounds _bookArray,change to
int a[6] = {0, 1, 2, 3, 4, 5 } fix it;
thx for ur code ,I learned a lot