For example, signed char is 8 bits, we can store from -128 to 127 using sign char.
A two's complement number system encodes positive and negative numbers in a binary number representation. The weight of each bit is a power of two.
The value $w$ of an $N$-bit integer $a_{N-1}a_{N-2}...a_{0}$ is given by the following formula.
$w = -a_{N-1}2^{N-1} + \sum_{i=0}^{N-2}a_i2^i$
The most significant bit determines the sign of the number and is sometimes called the sign bit $-(2^{N-1}$ shown above. Using $N$ bits, all integers from $-2^{N-1}$ to $2^{N-1}-1$ can be represented.