UGC NET Computer Science 1s Complement 2s Complement Previous Year Questions (PYQs)
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Showing 3 questions
In 16-bit 2's Complementation representation, the decimal number -28 is
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2
3
4
Solution
For positive number $28$,
$28 = \text{0000 0000 0001 1100}$
Option (c) represents $-28$.
For $-28$:
$28 = \text{0000 0000 0001 1100}$
$1's\ complement = \text{1111 1111 1110 0011}$
$2's\ complement = \text{1111 1111 1110 0100}$
Let $R_1$ and $R_2$ be two $4$-bit registers that store numbers in $2$'s complement form. For the operation $R_1+R_2$, which one of the following values of $R_1$ and $R_2$ gives an arithmetic overflow?
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2
3
4
Solution
In $4$-bit $2$'s complement, range is
$-8$ to $+7$
Check option (b):
$R_1=1100=-4$
$R_2=1010=-6$
So,
$R_1+R_2=-4+(-6)=-10$
But $-10$ is outside the range $-8$ to $+7$.
Therefore, arithmetic overflow occurs.
In computers, subtraction is generally carried out by:
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4
Solution
In computers, subtraction is generally performed using $2$'s complement method.
For subtracting $B$ from $A$, the computer takes the $2$'s complement of $B$ and adds it to $A$.
This makes subtraction possible using the same binary adder circuit used for addition.
Therefore, subtraction in computers is generally carried out by $2$'s complement.
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