Bitwise Operators problems
- 1. Assuming a integer 2-bytes, What will be the output of the program?
#include<stdio.h> int main() { printf("%x\n", -1<<3); return 0; }
Options- A. ffff
- B. fff8
- C. 0
- D. -1 Discuss
Correct Answer: fff8
Explanation:
The system will treat negative numbers in 2's complement method.
Example:
Assume the size of int is 2-bytes(16 bits). The integer value 1 is represented as given below:
Binary of 1: 00000000 00000001 (this is for positive value of 1)
1's complement of binary 1: 11111111 11111110
2's complement of binary 1: 11111111 11111111
Thy system will store '11111111 11111111' in memory to represent '-1'.
If we do left shift (3 bits) on 11111111 11111111 it will become as given below:
11111111 11111111 ---(left shift 3 times)---> 11111111 11111000.
So, 11111111 11111000 ---(binary to hex)---> FF F8. (Required Answer)
Note:
How is the negative number obtained from 2's complement value?
As stated above, -1 is represented as '11111111 11111111' in memory.
So, the system will take 2's complement of '11111111 11111111' to the get the original negative value back.
Example:
Bit Representation of -1: 11111111 11111111
Since the left most bit is 1, it is a negative number. Then the value is
1's complement: 00000000 00000000
2's complement: 00000000 00000001 (Add 1 to the above result)
Therefore, '00000000 00000001' = 1 and the sign is negative.
Hence the value is -1.
Example:
Assume the size of int is 2-bytes(16 bits). The integer value 1 is represented as given below:
Binary of 1: 00000000 00000001 (this is for positive value of 1)
1's complement of binary 1: 11111111 11111110
2's complement of binary 1: 11111111 11111111
Thy system will store '11111111 11111111' in memory to represent '-1'.
If we do left shift (3 bits) on 11111111 11111111 it will become as given below:
11111111 11111111 ---(left shift 3 times)---> 11111111 11111000.
So, 11111111 11111000 ---(binary to hex)---> FF F8. (Required Answer)
Note:
How is the negative number obtained from 2's complement value?
As stated above, -1 is represented as '11111111 11111111' in memory.
So, the system will take 2's complement of '11111111 11111111' to the get the original negative value back.
Example:
Bit Representation of -1: 11111111 11111111
Since the left most bit is 1, it is a negative number. Then the value is
1's complement: 00000000 00000000
2's complement: 00000000 00000001 (Add 1 to the above result)
Therefore, '00000000 00000001' = 1 and the sign is negative.
Hence the value is -1.
- 2. What will be the output of the program?
#include<stdio.h> int main() { unsigned char i = 0x80; printf("%d\n", i<<1); return 0; }
Options- A. 0
- B. 256
- C. 100
- D. 80 Discuss
Correct Answer: 256
- 3. Bitwise & and | are unary operators
Options- A. True
- B. False Discuss
Correct Answer: False
Explanation:
Bitwise & and | are not unary operators only bitwise ! is unary operator.
- 4. Left shifting a number by 1 is always equivalent to multiplying it by 2.
Options- A. True
- B. False Discuss
Correct Answer: True
Explanation:
0001 => 1
0010 => 2
0100 => 4
1000 => 8
0010 => 2
0100 => 4
1000 => 8
- 5. Bitwise & can be used to divide a number by powers of 2
Options- A. True
- B. False Discuss
Correct Answer: False
- 6. Bitwise & can be used to check if more than one bit in a number is on.
Options- A. True
- B. False Discuss
Correct Answer: True
- 7. In the statement expression1 >> expression2. if expression1 is a signed integer with its leftmost bit set to 1 then on right shifting it the result of the statement will vary from computer to computer
Options- A. True
- B. False Discuss
Correct Answer: True
- 8. Bitwise & can be used to check if a bit in number is set or not.
Options- A. True
- B. False Discuss
Correct Answer: True
- 9. Left shifting an unsigned int or char by 1 is always equivalent to multiplying it by 2.
Options- A. True
- B. False Discuss
Correct Answer: True
- 10. On left shifting, the bits from the left are rotated and brought to the right and accommodated where there is empty space on the right?
Options- A. True
- B. False Discuss
Correct Answer: False
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