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UGC NET Computer Science Previous Year Questions (PYQs)

UGC NET Computer Science 1s Complement 2s Complement PYQ

UGC NET Computer Science PYQ
In 16-bit 2's Complementation representation, the decimal number -28 is





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UGC NET Computer Science UGC NET PYQ UGC NET Computer Science UGC NET Computer Science Dec 2022 Shift I (Paper II) PYQ

Solution

For positive number $28$,

$28 = \text{0000 0000 0001 1100}$

Option (c) represents $-28$.

For $-28$:

$28 = \text{0000 0000 0001 1100}$

$1's\ complement = \text{1111 1111 1110 0011}$

$2's\ complement = \text{1111 1111 1110 0100}$
UGC NET Computer Science PYQ
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?





Go to Discussion
UGC NET Computer Science UGC NET PYQ UGC NET Computer Science UGC NET Computer Science Dec 2022 Shift I (Paper II) PYQ

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.
UGC NET Computer Science PYQ

In computers, subtraction is generally carried out by:






Go to Discussion
UGC NET Computer Science UGC NET PYQ UGC NET Computer Science UGC NET Computer Science Dec 2018 (Paper II) PYQ

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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