Set Clear Toggle a Specific Bit in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the bit at position pos in number n.

DSA Go

result := n | (1 << [1])

Drag options to blanks, or click blank then click option'

A1

Bn

Cpos

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Using n instead of pos for the shift.

Using AND instead of OR.

To set a bit, shift 1 left by pos and OR it with n.

2fill in blank

medium

Complete the code to clear the bit at position pos in number n.

DSA Go

result := n & ^(1 << [1])

Drag options to blanks, or click blank then click option'

Apos

Bresult

Cn

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Not inverting the mask before AND.

Using OR instead of AND.

To clear a bit, shift 1 left by pos, invert it, then AND with n.

3fill in blank

hard

Fix the error in the code to toggle the bit at position pos in number n.

DSA Go

result := n ^ (1 << [1])

Drag options to blanks, or click blank then click option'

An

B1

Cresult

Dpos

Attempts:

3 left

💡 Hint

Common Mistakes

Using n instead of pos for the shift.

Using OR or AND instead of XOR.

To toggle a bit, XOR n with 1 shifted left by pos.

4fill in blank

hard

Fill both blanks to set and then clear the bit at position pos in number n.

DSA Go

set := n | (1 << [1])
clear := set & ^(1 << [2])

Drag options to blanks, or click blank then click option'

Apos

Bn

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables for the bit position.

Not inverting the mask when clearing.

First set the bit by shifting 1 left by pos and OR with n. Then clear the same bit by AND with inverted mask.

5fill in blank

hard

Fill all three blanks to set, clear, and toggle the bit at position pos in number n.

DSA Go

set := n | (1 << [1])
clear := n & ^(1 << [2])
toggle := n ^ (1 << [3])

Drag options to blanks, or click blank then click option'

Apos

Dn

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables for bit positions.

Mixing up operators for set, clear, and toggle.

All three operations use the bit position pos shifted left by 1.

Practice

1. What does the operation num |= (1 << 3) do to the number num?

easy

A. Sets the 4th bit of num to 1

B. Clears the 4th bit of num to 0

C. Toggles the 4th bit of num

D. Checks if the 4th bit of num is set

Solution

1. Step 1: Understand bit shifting

   The expression 1 << 3 shifts 1 left by 3 bits, resulting in binary 00001000, which targets the 4th bit.

2. Step 2: Apply bitwise OR to set bit

   Using |= with this mask sets the 4th bit of num to 1 without changing other bits.

3. Final Answer:

   Sets the 4th bit of num to 1 -> Option A

4. Quick Check:

   Set bit = |= (1 << position) [OK]

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

Common Mistakes:

• Confusing set with clear operation
• Using wrong bit position (off by one)
• Thinking it toggles instead of sets

2. Which of the following Go code snippets correctly clears the 2nd bit (bit index 1) of an integer variable num?

easy

A. num &= (1 << 1)

B. num |= (1 << 1)

C. num &= ^(1 << 1)

D. num ^= (1 << 1)

Solution

1. Step 1: Identify clearing operation

   To clear a bit, we AND num with the inverse mask that has 0 at the target bit and 1 elsewhere.

2. Step 2: Use bitwise AND with negated mask

   ^(1 << 1) creates a mask with all bits 1 except the 2nd bit 0. ANDing clears that bit.

3. Final Answer:

   num &= ^(1 << 1) -> Option C

4. Quick Check:

   Clear bit = &= ^(1 << position) [OK]

Hint: Use AND with negated shifted 1 to clear bit [OK]

Common Mistakes:

• Using OR instead of AND to clear
• Not negating the mask
• Confusing bit index counting

3. What is the output of the following Go code?

package main
import "fmt"
func main() {
    num := 10 // binary 1010
    num ^= (1 << 1)
    fmt.Println(num)
}

medium

A. 10

B. 8

C. 12

D. 14

Solution

1. Step 1: Understand initial value and bit positions

   Number 10 in binary is 1010. Bit positions (0-based) from right: bit0=0, bit1=1, bit2=0, bit3=1.

2. Step 2: Toggle 2nd bit (bit index 1) using XOR

   XOR with (1 << 1) toggles bit1. Bit1 is 1, toggling it changes to 0. New binary: 1000 which is 8.

3. Final Answer:

   8 -> Option B

4. Quick Check:

   Toggle bit = ^= (1 << position) [OK]

Hint: XOR toggles bit: 1->0 or 0->1 [OK]

Common Mistakes:

• Confusing toggle with set or clear
• Misreading bit positions
• Calculating decimal incorrectly

4. The following Go code is intended to clear the 3rd bit (bit index 2) of num. What is the error?

num := 15
num &= (1 << 2)

medium

A. It sets the 3rd bit instead of clearing it

B. No error, it correctly clears the 3rd bit

C. It toggles the 3rd bit instead of clearing

D. It clears all bits except the 3rd bit

Solution

1. Step 1: Analyze the operation performed

   The code does num &= (1 << 2), which ANDs num with 00000100 (only 3rd bit set).

2. Step 2: Understand effect on bits

   This clears all bits except the 3rd bit, effectively keeping only the 3rd bit if it was set, not clearing it.

3. Final Answer:

   It clears all bits except the 3rd bit -> Option D

4. Quick Check:

   Clear bit = &= ^(1 << position) [OK]

Hint: Use AND with negated mask to clear bit [OK]

Common Mistakes:

• Using AND with mask instead of negated mask
• Confusing clear with set or toggle
• Assuming &= (1 << n) clears bit

5. You have an integer num initially 0. You want to toggle the 1st bit, set the 3rd bit, and clear the 2nd bit in this order. Which sequence of operations achieves this correctly in Go?

hard

A. num ^= (1 << 0); num |= (1 << 2); num &= ^(1 << 1)

B. num |= (1 << 0); num ^= (1 << 2); num &= ^(1 << 1)

C. num &= ^(1 << 1); num ^= (1 << 0); num |= (1 << 2)

D. num |= (1 << 2); num ^= (1 << 0); num &= ^(1 << 1)

Solution

1. Step 1: Toggle 1st bit (bit 0)

   Use XOR with (1 << 0) to toggle the 1st bit: num ^= (1 << 0).

2. Step 2: Set 3rd bit (bit 2)

   Use OR with (1 << 2) to set the 3rd bit: num |= (1 << 2).

3. Step 3: Clear 2nd bit (bit 1)

   Use AND with negated mask to clear 2nd bit: num &= ^(1 << 1).

4. Final Answer:

   num ^= (1 << 0); num |= (1 << 2); num &= ^(1 << 1) -> Option A

5. Quick Check:

   Toggle, Set, Clear in order with ^=, |=, &= ^ [OK]

Hint: Toggle ^=, Set |=, Clear &= ^ in correct order [OK]

Common Mistakes:

• Mixing order of operations
• Using wrong operators for each action
• Not negating mask when clearing