Why do you need signed and unsigned integer?

We need signed integers in order to represent both negative and positive values. However, some numbers can never be negative. For instance, the size of a file must always be greater than or equal to zero so we use unsigned integers to represent file sizes. Also, natural numbers must be greater than 0 so there's no point in using a signed value to represent a natural number. Signed integers also use one bit to denote the sign, but unsigned integers do not thus unsigned integers can effectively represent twice the range of positive values than an unsigned integer can. For instance, an 8-bit signed value can represent values in the range -128 to +127 using twos complement notation, but an 8-bit signed value can represent values in the range 0 to 255.