Ones' complement

value obtained by inverting all the bits in the binary representation of the number

The One's complement is an operation that can be done to binary numbers. It is obtained by swapping all the bits in the number, that is, replacing 1 with 0, or 0 with 1. In many systems, this is used to represent the inverse of a number. One of the big problems that occur when using One's complement is that the number zero has two representations, either all 0's or all 1's. Using 4 digits both 0000 and 1111 represent zero. This problem can be solved by using Two's complement.