I'm just starting to learn about representing numbers in sign-and-magnitude and two's complement, and both as signed binary integers two's complement if representing a negative number I should invert all bits and add one, while sign-and-magnitude represents negative numbers with the first bit as a sign bit, but is it possible whether I can tell if a number is represented in sign-and magnitude or two's complement from just looking at it?

  • $\begingroup$ Only looking at binary you cannot even say is it signed or unsigned. Everything depends on interpretation. This is why we need types. $\endgroup$
    – zkutch
    Jun 19, 2022 at 6:08
  • $\begingroup$ (Only looking at a binary representation of an integer I couldn't tell little endian from big endian, unsigned from signed. And in addition to signed and two's complement, there's biased and some more representations that have fallen out of favour (for a reason).) Interpretation is the difference. $\endgroup$
    – greybeard
    Jun 19, 2022 at 8:24

1 Answer 1


Every string of bits can be interpreted both as a two's complement or a sign-and-magnitude number. So the answer is clearly no.

[Usually, sign-and-magnitude allow negative zero; if not in your context, then you could say that $100\cdots0$ is a two's complement number, anyway.]


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