C Programming - Structures, Unions, Enums - Discussion

Discussion Forum : Structures, Unions, Enums - Find Output of Program (Q.No. 3)
3.
What will be the output of the program ?
#include<stdio.h>

int main()
{
    struct value
    {
        int bit1:1;
        int bit3:4;
        int bit4:4;
    }bit={1, 2, 13};

    printf("%d, %d, %d\n", bit.bit1, bit.bit3, bit.bit4);
    return 0;
}
1, 2, 13
1, 4, 4
-1, 2, -3
-1, -2, -13
Answer: Option
Explanation:

Note the below statement inside the struct:

int bit1:1; --> 'int' indicates that it is a SIGNED integer.

For signed integers the leftmost bit will be taken for +/- sign.

If you store 1 in 1-bit field:

The left most bit is 1, so the system will treat the value as negative number.

The 2's complement method is used by the system to handle the negative values.

Therefore, the data stored is 1. The 2's complement of 1 is also 1 (negative).

Therefore -1 is printed.


If you store 2 in 4-bits field:

Binary 2: 0010 (left most bit is 0, so system will treat it as positive value)

0010 is 2

Therefore 2 is printed.


If you store 13 in 4-bits field:

Binary 13: 1101 (left most bit is 1, so system will treat it as negative value)

Find 2's complement of 1101:

1's complement of 1101 : 0010
2's complement of 1101 : 0011 (Add 1 to the result of 1's complement)

0011 is 3 (but negative value)

Therefore -3 is printed.

Discussion:
24 comments Page 1 of 3.

Hossam Ahmed said:   4 months ago
Bit1 will be stored in the rightmost bit, not the leftmost bit. So it is away from the bit responsible for the Negative sign!

Mahi said:   4 years ago
Bit1: 1 means it will be stored only one bit like (eg: 1 binary stored in 1 bit only).

So in a first bit it will take left as well as right most bit is 1 because here only 1 bit memory available.

Bit2: 4 means it will be stored 4 bit like (eg: 2 binary stored in 4 bit only).

So 4 = 0100, here left most bit is 0 that's why we didn't took 2's complement here and print value 2 as is it.

Bit3: 4 means it will be also stored 4 bit like (eg: 13 binary stored in 4 bit only).

So 13 = 1101, here left most bit is 1 that's why we took 2's complement here and print changeable value.
(4)

Narsi said:   5 years ago
Thanks @Priya.

Sanjana said:   6 years ago
@Mansi,

As you are calculating the two's complement of 13 that it's a negative number and hence you will have to append a negative sign in the answer.

Mansi said:   6 years ago
I didn't get the "If you store 13 in 4-bits field" part.
Binary 13: 1101 (left most bit is 1, so system will treat it as negative value)

Find 2's complement of 1101:
1's complement of 1101 : 0010
2's complement of 1101 : 0011 (Add 1 to the result of 1's complement)
0011 is 3 (but negative value)

Therefore -3 is printed.

WHY -3? The leftmost digit is 0 so it should be 3 right?

Sudha said:   7 years ago
The bit 1:1 occupies only 1 bit.

Let's assume bit1=1 (0001)its 2's compliment is (1111) leftmost bit represents -ve value.

Ayushi said:   9 years ago
The left most bit in int bit 1:1 is 0. So how can it can be treated as a negative number?

Because 1 is expressed as 0001 in binary. Please explain this.

Gowtham said:   9 years ago
Why 1's and 2's complement taken in this problem?

Vek said:   9 years ago
I am unable to understand this program. I would like to understand this program.

So can any body help me?

Remember me!! said:   1 decade ago
WHAT IS BIT FIELD AND WHY BIT FIELD?

Example:

a = 2 = 0010
In bit field "int a:2" means you just use 2 bit value of 0010
therefore,
int a:2 = 10.

Another example:

In bit field "int a:3" means you just use 3 bit value of 0010
therefore,

int a:2 =010.


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