computer stores number on one/two's complemental code method. true code, complemental code and one's complement code of unsigned number are all equel;
For example, 10 (decimal) are all 00001010；

But -10(decimal):
true code：10001010 ('+' is 0, '-' is 1）

complemental code：11110101 sign bit doesn't change, rest all of bits ~

two's complemental code：11110110 base on complemental code plus 1