For an example of signed overflow versus unsigned overflow, certain compilers are known to assume that int loop variables won't overflow. So "for (int i = 0; i != -1; ++i)" is transformed into "for (int i = 0; ; ++i)", since both are equal in the eyes of the C standard (both will iterate through all non-negative values that fit in an int, then both will invoke undefined behavior, so they are the same).

The funny part is that it's often better to use int exactly because of the undefined behavior on overflow. By signaling to the compiler that you don't intend to overflow a particular variable, it can optimize appropriately.