Answer
$-0 0 1 1$.
Work Step by Step
$$\text{Solution}$$
Here $A = 1000, B = 1011.$
Find $A - B = ?$ using 1's complement
$\rightarrow$ First, find 1's complement of $B = 1011$
$\rightarrow $ Write out the numbers as if you were subtracting decimals.
$$-\begin{array}{c|c}
1000 \\
1011 \\
\hline
\end{array}$$
$\rightarrow $ Let's use the 1's Complement Method
$\rightarrow $ 1's complement of a number is obtained by subtracting all bits from $11$
$\rightarrow $ $\text{1's complement of 1011 is}$
$$-\begin{array}{r|r}
1 1 1 1 \\
1 0 1 1\\
\hline
0 1 0 0
\end{array}$$
$\rightarrow $ Now Add this 1's complement of B to A
Note $\rightarrow$ Addition Rules
$0 + 0 = 0$
$0 + 1 = 1$
$1 + 0 = 1$
$1 + 1 = 10$ ("$0$" in the column, carry $1$ to the next bit)
So,
$$+\begin{array}{r|r}
1 0 0 0 \\
0 1 0 0 \\
\hline
1 1 0 0
\end{array}$$
$\rightarrow$ Here there is no carry, the answer is - (1's complement of the sum obtained $1100$)
1's complement of $1100$ is
$$+\begin{array}{r|r}
1 1 1 1\\
1 1 0 0\\
\hline
0 0 1 1
\end{array}$$
so the Answer is $-0 0 1 1$.
