A two's complement binary number can be positive or negative. We want to be able to convert such a number to the opposite value (from positive to negative or negative to positive). We will convert a negative number to a positive number to convert it to decimal. Here, we see how to convert from negative to positive or positive to negative. Given the initial number, flip all of the bits (a 0 becomes a 1, a 1 becomes a 0) and then add 1. Here is an example.