Change the sign of a signed number signed-magnitude change the sign-bit; +21:00010101-21:10010101 one's complement: change every bit; +21:00010101-21:11101010 two’ s complement: change every bit, and add l at lsB +21:00010101-21:11101010 note: keep the width of the string in additionChange the sign of a signed number signed-magnitude : change the sign-bit; +21: 0001 0101 -21: 1001 0101 one’s complement: change every bit; +21: 0001 0101 -21: 1110 1010 two’s complement: change every bit, and add 1 at LSB; +21: 0001 0101 -21: 1110 1010 note: keep the width of the string in addition !