在计算机运算中，有符号数的表示需要将负数编码为二进制形式。

在数学中，任意基数的负数都在最前面加上“−”符号来表示。然而在计算机硬件中，数字都以无符号的二进制形式表示，因此需要一种编码负号的方法。当前有四种方法，用于扩展二进制数字系统，来表示有符号数：原码（sign-and-magnitude），反码（ones' complement），补码（two's complement），以及移码excess-N。

In computing, signed number representations are required to encode negative numbers in binary number systems.

In mathematics, negative numbers in any base are represented by prefixing them with a minus ("−") sign. However, in computer hardware, numbers are represented only as sequences of bits, without extra symbols. The four best-known methods of extending the binary numeral system to represent signed numbers are: sign-and-magnitude, ones' complement, two's complement, and excess-K. Some of the alternative methods use implicit instead of explicit signs, such as negative binary, using the base −2. Corresponding methods can be devised for other bases, whether positive, negative, fractional, or other elaborations on such themes.