C Programming - Structures, Unions, Enums - Discussion

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

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

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.

24 comments Page 3 of 3.

Nikhil said:   1 decade ago
What is this "int bit1:1;" means?

I can't understand please anyone help me ?

Yoge said:   1 decade ago
int bit1:1 means that only 1 bit of memory is allocated for the variable bit1, bit fields are used to save memory, whenever a variable holds small value you need not allocate the integer size of 2 bytes.

Meril said:   1 decade ago
What is this "int bit1:1;" means?

Please help!

Krishna said:   1 decade ago
I am not understanding this explanation please give brief explanation.

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