Bitwise Operators in C

Last Updated on: January 6th, 2023

This is an important topic for interviews in the embedded domain. In this tutorial, we will see  Bitwise Operators in C and its Interview questions. We can also call this as a bit manipulation in C.

You can also read embedded interview topics, number complement programs in c, Pointers in C, and Stringizing, token pasting operator in C.

Bitwise Operators

Bitwise AND operator (&)

The output of bitwise AND is 1 if the corresponding bits of both operands are 1. If either bit of an operand is 0, the result of the corresponding bit is evaluated to 0.

Let us consider the example, the bitwise AND operation of two integers 36 and 13.

36 = 00100100 (In Binary)
13 = 00001101  (In Binary)

Bit Operation of 36 and 13

00100100
00001101                          (&)
________________
00000100 = 4 (In decimal)

Bitwise OR operator (|)

The output of bitwise OR is 1 if at least one corresponding bit of two operands is 1. In C Programming, the bitwise OR operator is denoted by |.

Let us consider the example, the bitwise OR operation of two integers 36 and 13.

36 = 00100100 (In Binary)
13 = 00001101  (In Binary)

Bit Operation of 36 and 13

00100100
00001101                          (|)
________________
00101101 = 45 (In decimal)

Bitwise XOR (exclusive OR) operator (^)

The result of the bitwise XOR operator is 1 if the corresponding bits of two operands are opposite. It is denoted by ^.

36 = 00100100 (In Binary)
13 = 00001101  (In Binary)

Bit Operation of 36 and 13

00100100
00001101                          (^)
________________
00101001 = 41 (In decimal)

Bitwise complement operator (~)

Bitwise complement operator is a unary operator (works on only one operand). It changes 1 to 0 and 0 to 1. It is denoted by ~.

Right Shift Operator

The Right shift operator shifts all bits towards the right by a certain number of specified bits. It is denoted by >>.

212 = 11010100 (In binary)
212>>2 = 00110101 (In binary) [Right shift by two bits]
212>>7 = 00000001 (In binary)
212>>8 = 00000000
212>>0 = 11010100 (No Shift)

Left Shift Operator

The Left shift operator shifts all bits towards the left by a certain number of specified bits. It is denoted by <<.

212 = 11010100 (In binary)
212<<1 = 110101000 (In binary) [Left shift by one bit]
212<<0 =11010100 (Shift by 0)
212<<4 = 110101000000 (In binary) =3392(In decimal)

That is all about the Bitwise operator. Now, we will see the common questions asked in the interview.

Bitwise Operators in C Interview Questions

1. How to set a particular bit in a variable or Register?

To set any bit in a variable, Use the OR operator.

A = A | (1<<4)         (or)        A |= (1<<4) 

2. How to clear a particular bit in a number?

unsigned int rangeToggle(unsigned int num, unsigned int i , unsigned int j)
{
  return num ^ ((1<<(j-i)+1)-1)<<i;
}

To check any bit in a variable, Use (& ) And Operator.

Variable & (1<<x)

‘x‘ indicates the position of the bit

Example: Check the 3rd bit is set or not.

if((variable & (1<<3)) == 0) {
    "bit is not set"
} else {
    "bit is set"
}

6. How to represent the above all things in MACRO for Real time code?

#define SET_BIT(Variable, bit_position)    Variable |= (1<< bit_position) 

#define CLEAR_BIT(Variable, bit_position)    Variable &= ~(1<< bit_position) 

#define TOGGLE_BIT(Variable, bit_position)    Variable ^= (1<< bit_position) 

#define CHECK_BIT_IS_SET_OR_NOT(Variable, bit_position)    Variable & (1<< bit_position)

7. Write MACRO to Swap the bytes in 16bit Integer Variable.

#define ByteSwap16(Value) ((Value & 0x00FF) << 8) | ((Value & 0xFF00) >> 8)

8. Write MACRO to Swap the bytes in 32bit Integer Variable.

#define ByteSwap32(Value) ((Value & 0x000000FF) << 24) |
                                  ((Value & 0x0000FF00U) <<  8) |
                                  ((Value & 0x00FF0000U) >>  8) |
                                  ((Value & 0xFF000000U) >> 24)

9. Write MACRO to Swap the bytes in 64bit Integer Variable.

#define ByteSwap64(Value)   ((Value & 0x00000000000000FFU) << 56) | 
                                ((Value & 0x000000000000FF00U) << 40) | 
                                ((Value & 0x0000000000FF0000U) << 24) | 
                                ((Value & 0x00000000FF000000U) <<  8) | 
                                ((Value & 0x000000FF00000000U) >>  8) | 
                                ((Value & 0x0000FF0000000000U) >> 24) | 
                                ((Value & 0x00FF000000000000U) >> 40) | 
                                ((Value & 0xFF00000000000000U) >> 56)

10. Find whether the number is odd or even

void odd_even( uint8_t  number )
{
  if( number & 1 )
  {
    printf(" Number is Odd\r\n");
  }
  else
  {
    printf(" Number is Even\r\n");
  }
}

11. Clear the last right side set bit of a number

For example, take the number 144. The equivalent binary format is 10010000. So, the output should be 10000000 which is 128 in decimal.

uint8_t remove_last_set_bit( uint8_t  number )
{
    return (n & (n - 1));
}

12.Check if the number is a power of 2

void powerOf2( uint8_t  number ) 
{
  if(n & (n - 1))
  {
    printf("Number is not power Of 2");
  }
  else
  {
    printf("Number is power Of 2");
  }
}

13. Count the number of set bits in a number

unsigned int countSetBits( unsigned int number ) 
{
  unsigned int count = 0;
  while( number != 0)
  {
    count++;
    number &= (number-1);
  }

  return count;
}

14. Swap two bits at a given position in an integer

unsigned int swapBits( unsigned int number, unsigned int i, unsigned int j ) 
{
  number ^= (1 << i);
  number ^= (1 << j);
  
  return number;
}

15. Swap all even and odd bits

For example, take the number 154. The equivalent binary format is 10011010. So, the output should be 01100101 which is 101 in decimal.

unsigned int swapOddEvenBits( unsigned int number ) 
{
  return ( ( number & 0xAAAAAAAA ) >> 1 ) | ( ( number & 0x55555555 ) << 1 );
}

You can also read the below tutorials.

SLR

Embedded Software | Firmware | Linux Devic Deriver | RTOS

Hi, I’m SLR. I am a tech blogger and an Embedded Engineer. I am always eager to learn and explore tech-related concepts. And also, I wanted to share my knowledge with everyone in a more straightforward way with easy practical examples. I strongly believe that learning by doing is more powerful than just learning by reading. I love to do experiments. If you want to help or support me on my journey, consider sharing my articles, or Buy me a Coffee! Thank you for reading my blog! Happy learning!