C++/Bitwise Operations Programs/Program

Check and Set Bits

Check if Bit is Set and Set/Clear Bits in C++

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#include <iostream>
#include <bitset>
using namespace std;

bool isBitSet(int num, int pos) {
    return (num & (1 << pos)) != 0;
}

int setBit(int num, int pos) {
    return num | (1 << pos);
}

int clearBit(int num, int pos) {
    return num & ~(1 << pos);
}

int toggleBit(int num, int pos) {
    return num ^ (1 << pos);
}

int main() {
    int num = 12;  // 00001100
    
    cout << "Original number: " << bitset<8>(num) << " (" << num << ")" << endl;
    
    // Check bits
    cout << "\nChecking bits:" << endl;
    for (int i = 0; i < 8; i++) {
        cout << "Bit " << i << ": " << (isBitSet(num, i) ? "SET" : "CLEAR") << endl;
    }
    
    // Set bit 0
    num = setBit(num, 0);
    cout << "\nAfter setting bit 0: " << bitset<8>(num) << " (" << num << ")" << endl;
    
    // Clear bit 2
    num = clearBit(num, 2);
    cout << "After clearing bit 2: " << bitset<8>(num) << " (" << num << ")" << endl;
    
    // Toggle bit 3
    num = toggleBit(num, 3);
    cout << "After toggling bit 3: " << bitset<8>(num) << " (" << num << ")" << endl;
    
    return 0;
}

Output

Original number: 00001100 (12)

Checking bits:
Bit 0: CLEAR
Bit 1: CLEAR
Bit 2: SET
Bit 3: SET
Bit 4: CLEAR
Bit 5: CLEAR
Bit 6: CLEAR
Bit 7: CLEAR

After setting bit 0: 00001101 (13)
After clearing bit 2: 00001001 (9)
After toggling bit 3: 00000001 (1)

This program teaches you how to Check and Set Bits in C++. These operations are fundamental for bit manipulation, allowing you to check if a specific bit is set, set a bit, clear a bit, or toggle a bit. These operations are essential for flags, permissions, and efficient data structures.

1. What This Program Does

The program demonstrates bit manipulation operations:

  • Checking if a specific bit is set
  • Setting a bit to 1
  • Clearing a bit to 0
  • Toggling a bit (flip value)

Bit manipulation enables efficient flag and permission management.

2. Header Files Used

  1. #include <iostream>

    • Provides cout and cin for input/output operations.

  2. #include <bitset>

    • Provides bitset for binary representation display.

3. Understanding Bit Manipulation

Bit Position Concept:

  • Bits numbered from right (0-indexed)
  • Position 0: rightmost bit (LSB)
  • Position n-1: leftmost bit (MSB)
  • Each position represents 2^position

Common Operations:

  • Check: is bit set?
  • Set: make bit 1
  • Clear: make bit 0
  • Toggle: flip bit value

4. Checking if Bit is Set

Operation:

bool isBitSet(int num, int pos) { return (num & (1 << pos)) != 0; }

How it works:

  • 1 << pos: creates mask with bit at position pos set
  • num & mask: extracts bit at position
  • != 0: checks if bit is set
  • Returns true if bit is 1

Example:

  • num = 12 (00001100), pos = 2
  • 1 << 2 = 4 (00000100)
  • 12 & 4 = 4 (bit 2 is set)

5. Setting a Bit

Operation:

int setBit(int num, int pos) { return num | (1 << pos); }

How it works:

  • 1 << pos: creates mask with bit at position pos
  • num | mask: sets bit at position
  • OR operation sets bit to 1
  • Other bits unchanged

Example:

  • num = 12 (00001100), pos = 0
  • 1 << 0 = 1 (00000001)
  • 12 | 1 = 13 (00001101)

6. Clearing a Bit

Operation:

int clearBit(int num, int pos) { return num & ~(1 << pos); }

How it works:

  • 1 << pos: creates mask with bit at position pos
  • ~mask: inverts mask (all 1s except position pos)
  • num & ~mask: clears bit at position
  • AND operation clears bit to 0

Example:

  • num = 12 (00001100), pos = 2
  • 1 << 2 = 4 (00000100)
  • ~4 = 251 (11111011)
  • 12 & 251 = 8 (00001000)

7. Toggling a Bit

Operation:

int toggleBit(int num, int pos) { return num ^ (1 << pos); }

How it works:

  • 1 << pos: creates mask with bit at position pos
  • num ^ mask: flips bit at position
  • XOR operation toggles bit
  • 0 becomes 1, 1 becomes 0

Example:

  • num = 12 (00001100), pos = 3
  • 1 << 3 = 8 (00001000)
  • 12 ^ 8 = 4 (00000100)

8. When to Use Bit Manipulation

Best For:

  • Flags and permissions
  • Efficient data structures
  • Memory optimization
  • System programming
  • Performance-critical code

Example Scenarios:

  • File permissions (read, write, execute)
  • Feature flags
  • State machines
  • Bit arrays
  • Compression algorithms

9. Important Considerations

Bit Position:

  • Usually 0-indexed from right
  • Position 0: least significant bit
  • Be careful with position values
  • Validate position range

Efficiency:

  • Very fast operations
  • Single CPU instruction
  • No loops needed
  • Optimal performance

Readability:

  • Can be less readable
  • Document operations
  • Use helper functions
  • Clear variable names

10. return 0;

This ends the program successfully.

Summary

  • Check bit: num & (1 << pos) != 0, checks if bit at position is set.
  • Set bit: num | (1 << pos), sets bit at position to 1.
  • Clear bit: num & ~(1 << pos), clears bit at position to 0.
  • Toggle bit: num ^ (1 << pos), flips bit at position.
  • Understanding bit manipulation enables efficient flag and permission management.
  • Essential for flags, permissions, efficient data structures, and system programming.

This program is fundamental for learning bit manipulation, understanding efficient data structures, and preparing for system programming and optimization in C++ programs.

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Basic Bitwise Operations
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Count Set Bits