Question

This is the code:

int index = (gridPoint.y * self.iconsPerRow) + gridPoint.x;
    NSLog(@"index 1: %i", index);
    NSLog(@"count: %i", [self.icons count] - 1);
    if (index > [self.icons count] - 1) {
        index = [self.icons count] - 1;
    }
    if (index < 0) {
        index = 0;
    }
    NSLog(@"index 2: %i", index);

Output:

NSLog index 1: -4
NSLog count: 3
NSLog index 2: 3

Any ideas why this is happening? It should be resulting in 0 if it’s a minus number.

Answer 1

It’s because [self.icons count]; returns an NSUInteger (index is converted to an unsigned int, which will wrap around to UINT_MAX-3). Change it to the following:

int index = (gridPoint.y * self.iconsPerRow) + gridPoint.x;
NSLog(@"index 1: %i", index);
NSLog(@"count: %i", [self.icons count] - 1);
if (index < 0) {
    index = 0;
} else if (index + 1 > [self.icons count]) { // In case count is 0, we add to index rather than subtract from count
    index = [self.icons count] - 1;
}
NSLog(@"index 2: %i", index);