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    why is the complement of 6 = 11111010?
    i understand how to get the figure, but not why i get that figure
    ***this is straight from my text, so it is right
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    How two's complement works:
    Take positive number as binary value
    Subtract 1 from it
    Flip the bits

    Thus, 6 goes:
    6: 00000110
    6-1: 00000101
    flip: 11111010

    The reasons for this are pretty arbitrary -- two's complement is an entirely artificial system for representing a negative number that's just used because it has some useful properties, namely:
    1) You get as many negative as positive numbers
    2) It's simple
    3) Every positive number has a negative equivalent in the same number of bits (a stricter version of (1), really).

    There are probably several other reasons for it that I haven't thought off of the top of my head.

    Just out of interest, why do you need to know about two's complement for 'Beginner' web work? :-)

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