0xffff, how come no one is right? This is a hexadecimal number. The data range of each bit is 0 1 2 3 4 5 6 7 8 9 A B C D E F, where f means 15, 0xffff = 15 * 16 cubic+15* 16 square+/kloc. So -0xffff=-65535, the reason why 16 is used is because binary conversion is convenient. F (16) =11(2), you should be familiar with numerical conversion, composition principle and assembly, and so on.