You should also be aware of integer conversion rules when dealing with NSUInteger vs. NSInteger:
The following fragment for example returns 0 (false) although you’d expect it to print 1 (true):
NSInteger si = -1;
NSUInteger ui = 1;
printf("%d\n", si < ui);
The reason is that the [si] variable is being implicitly converted to an unsigned int!
See CERT’s Secure Coding site for an in-depth discussion around these ‘issues’ and how to solve them.