How can you represent a negative integer in a computer system?

Answer 1

There are many different ways this can be done using binary form:

• signed magnitude, one bit is the sign (i.e. 0=+, 1=-) and the other bits are the magnitude of the number (this is analogous to how we write negative integers on paper)
• ones complement, invert every bit of the magnitude of a number to get its negative form
• twos complement, invert every bit of the magnitude of a number then add one to get its negative form (most computers now use this form as the arithmetic circuits to do calculations in this form are simpler and thus less expensive than for the other two.

There are also corresponding ways this can be done using decimal forms (e.g. BCD, 2 of 5, excess-3)

• signed magnitude, one bit or digit is the sign (i.e. 0=+, 9=-) and the other digits are the magnitude of the number (this is analogous to how we write negative integers on paper)
• nines complement, subtract every digit of the magnitude of the number from 9 to get its negative form
• tens complement, subtract every digit of the magnitude of the number from 9 then add one to get its negative form