Different results for the same function

Can someone clarify to me please 开发者_StackOverflow中文版why past2 is NOT negative when this code is run? Even though past is.

Thanks.

NSTimeInterval p1 = (arc4random()%600000);
NSTimeInterval past = -p1;
NSTimeInterval past2 = -(arc4random()%600000);

arc4random() returns an unsigned int (u_int32_t), so trying to make it negative is coercing the result to unsigned as well, which is why you're getting a very large positive number instead of a negative number.

If you want to get a negative random result in one call, try:

NSTimeInterval past2 = - (int) (arc4random()%600000);

joe