Set Clear Toggle a Specific Bit in DSA C# - Build from Scratch

Set Clear Toggle a Specific Bit

📖 Scenario: Imagine you are working with a simple device that uses a number to represent different settings. Each setting is controlled by a single bit in this number. You want to learn how to change these bits to turn settings on, off, or switch them.

🎯 Goal: You will create a program that can set, clear, or toggle a specific bit in a number. This helps you control individual settings easily.

📋 What You'll Learn

Create an integer variable called number with the value 42.

Create an integer variable called bitPosition with the value 3.

Create an integer variable called mask that has a 1 only at the bitPosition.

Create three integer variables called setBit, clearBit, and toggleBit.

Use bitwise operations to set, clear, and toggle the bit at bitPosition in number.

Print the values of setBit, clearBit, and toggleBit.

💡 Why This Matters

🌍 Real World

Controlling individual settings or flags in devices, games, or software often uses bit manipulation to save space and increase speed.

💼 Career

Understanding bitwise operations is important for roles in embedded systems, game development, and performance-critical software engineering.

1

Create the initial number and bit position

Create an integer variable called number and set it to 42. Then create an integer variable called bitPosition and set it to 3.

DSA C#

// Your code here

Hint

Use int number = 42; and int bitPosition = 3; to create the variables.

2

Create a mask for the bit position

Create an integer variable called mask that has a 1 only at the bitPosition. Use the left shift operator (1 << bitPosition).

DSA C#

int number = 42;
int bitPosition = 3;
// Your code here

Hint

Use int mask = 1 << bitPosition; to create the mask.

3

Set, clear, and toggle the bit

Create three integer variables called setBit, clearBit, and toggleBit. Use bitwise OR | to set the bit, bitwise AND with NOT & ~ to clear the bit, and bitwise XOR ^ to toggle the bit in number using mask.

DSA C#

int number = 42;
int bitPosition = 3;
int mask = 1 << bitPosition;
// Your code here

Hint

Use setBit = number | mask;, clearBit = number & ~mask;, and toggleBit = number ^ mask;.

4

Print the results

Print the values of setBit, clearBit, and toggleBit each on a new line using Console.WriteLine.

DSA C#

int number = 42;
int bitPosition = 3;
int mask = 1 << bitPosition;
int setBit = number | mask;
int clearBit = number & ~mask;
int toggleBit = number ^ mask;
// Your code here

Hint

Use Console.WriteLine(setBit);, Console.WriteLine(clearBit);, and Console.WriteLine(toggleBit);.

Practice

1. What does the operation number |= (1 << position) do to the bit at position in number?

easy

A. Toggles the bit at position

B. Clears the bit at position to 0

C. Sets the bit at position to 1

D. Checks if the bit at position is set

Solution

1. Step 1: Understand the bitwise OR with shifted 1

   The expression 1 << position creates a number with only the bit at position set to 1. Using OR (|=) with this sets that bit in number to 1 without changing other bits.

2. Step 2: Effect on the bit at position

   Since OR with 1 always results in 1, the bit at position is set to 1 regardless of its previous value.

3. Final Answer:

   Sets the bit at position to 1 -> Option C

4. Quick Check:

   OR with 1 sets bit [OK]

Hint: Use OR with shifted 1 to set a bit [OK]

Common Mistakes:

• Confusing OR with XOR for toggling
• Thinking it clears the bit
• Assuming it checks the bit instead

2. Which of the following C# statements correctly clears (sets to 0) the bit at position pos in an integer num?

easy

A. num &= ~(1 << pos);

B. num |= (1 << pos);

C. num ^= (1 << pos);

D. num = num << pos;

Solution

1. Step 1: Understand clearing a bit

   To clear a bit, we use AND with the complement of a mask that has 1 at the target bit. The mask is 1 << pos, so complement is ~(1 << pos).

2. Step 2: Apply AND with complemented mask

   Using num &= ~(1 << pos); clears the bit at pos while leaving others unchanged.

3. Final Answer:

   num &= ~(1 << pos); -> Option A

4. Quick Check:

   AND with complement clears bit [OK]

Hint: Use AND with NOT mask to clear a bit [OK]

Common Mistakes:

• Using OR instead of AND to clear
• Using XOR which toggles instead of clears
• Using left shift alone which changes number

3. What is the output of the following C# code?

int num = 10; // binary 1010
int pos = 1;
num ^= (1 << pos);
Console.WriteLine(num);

medium

A. 10

B. 14

C. 12

D. 8

Solution

1. Step 1: Understand initial number and bit position

   Number 10 in binary is 1010. Position 1 means the second bit from right (0-based). Bit at position 1 is 1.

2. Step 2: Apply XOR to toggle bit at position 1

   XOR toggles the bit. Since bit at position 1 is 1, toggling it changes it to 0. New binary is 1000 which is decimal 8.

3. Final Answer:

   8 -> Option D

4. Quick Check:

   Toggle bit 1 in 1010 = 1000 = 8 [OK]

Hint: XOR toggles bit; 1 becomes 0, 0 becomes 1 [OK]

Common Mistakes:

• Confusing XOR with OR or AND
• Miscounting bit positions (0-based)
• Assuming no change if bit is 1

4. The following code is intended to toggle the bit at position pos in num. What is the error?

int num = 5; // binary 0101
int pos = 2;
num = num & (1 << pos);
Console.WriteLine(num);

medium

A. It clears all bits except the one at pos

B. It toggles the bit correctly

C. It sets the bit at pos to 1

D. It causes a syntax error

Solution

1. Step 1: Analyze the operation used

   The code uses AND (&) with 1 << pos. This keeps only the bit at pos if it was set, clearing all others.

2. Step 2: Compare with toggle operation

   Toggling requires XOR (^), not AND. So this code does not toggle but masks all bits except the one at pos.

3. Final Answer:

   It clears all bits except the one at pos -> Option A

4. Quick Check:

   AND with mask keeps only that bit [OK]

Hint: Use XOR to toggle, AND masks bits [OK]

Common Mistakes:

• Using AND instead of XOR for toggle
• Expecting toggle but getting masked value
• Confusing bitwise operators

5. You have an integer num and want to toggle the bit at position pos only if it is currently set (1). Which code snippet correctly does this?

hard

A. if ((num ^ (1 << pos)) != 0) num ^= (1 << pos);

B. if ((num & (1 << pos)) != 0) num ^= (1 << pos);

C. if ((num & ~(1 << pos)) != 0) num ^= (1 << pos);

D. if ((num | (1 << pos)) != 0) num ^= (1 << pos);

Solution

1. Step 1: Check if bit at pos is set

   Using num & (1 << pos) checks if bit at pos is 1. If result is not zero, bit is set.

2. Step 2: Toggle bit only if set

   If bit is set, toggle it using XOR: num ^= (1 << pos);. This flips the bit from 1 to 0.

3. Final Answer:

   if ((num & (1 << pos)) != 0) num ^= (1 << pos); -> Option B

4. Quick Check:

   Check bit with AND, toggle with XOR [OK]

Hint: Check bit with AND before toggling with XOR [OK]

Common Mistakes:

• Using OR instead of AND to check bit
• Toggling without checking bit first
• Using incorrect mask complement