Set Clear Toggle a Specific Bit in DSA Python - Execution Trace

Concept Flow - Set Clear Toggle a Specific Bit

Start with number n

↓

Choose bit position p

↓

Select operation: Set / Clear / Toggle

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Create mask = 1 << p

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If Set: n = n | mask

↓

If Clear: n = n & ~mask

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If Toggle: n = n ^ mask

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Result: n with bit p changed

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End

This flow shows how to change a specific bit in a number by creating a mask and applying bitwise operations to set, clear, or toggle that bit.

Execution Sample

DSA Python

n = 13  # binary 1101
p = 2
mask = 1 << p
n = n | mask
print(bin(n))

This code sets the bit at position 2 of number 13 (binary 1101), turning it on.

Execution Table

Step	Operation	Number (decimal)	Number (binary)	Mask (binary)	Bit Position	Pointer Changes	Visual State (binary)
1	Start with n	13	1101	-	-	-	1101
2	Choose bit position p	13	1101	-	2	-	1101
3	Create mask = 1 << p	13	1101	100	2	-	1101
4	Set bit: n = n | mask	13	1101	100	2	n updated	1101
5	Print result	13	1101	100	2	-	1101
6	End	13	1101	100	2	-	1101

💡 Bit at position 2 was already set; number remains 13 (binary 1101)

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
n	13 (1101)	13 (1101)	13 (1101)	13 (1101)
p	-	2	2	2
mask	-	4 (100)	4 (100)	4 (100)

Key Moments - 3 Insights

Why does the number not change after setting bit 2 in this example?

Because in execution_table row 4, the bit at position 2 was already 1 in the original number (1101), so OR with mask 100 keeps it the same.

What does the mask 1 << p represent?

As shown in execution_table row 3, mask shifts 1 left by p positions to create a binary number with only the target bit set, used to change that bit.

How do we clear or toggle a bit differently?

Instead of OR (|) for set, use AND with NOT (~) mask to clear, or XOR (^) with mask to toggle, as described in concept_flow.

Visual Quiz - 3 Questions

Look at execution_table row 3, what is the binary mask created for bit position 2?

A 0010

B 0100

C 1000

D 0001

💡 Hint

Check the 'Mask (binary)' column in row 3 of execution_table

At which step does the number n get updated with the new bit set?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look at the 'Operation' and 'Pointer Changes' columns in execution_table

If the bit at position 2 was 0 initially, what would be the visual state after setting it?

A 1111

B 1001

C 1101

D 0101

💡 Hint

Setting bit 2 means turning that bit to 1; check how OR operation affects bits in execution_table

Concept Snapshot

Set, Clear, Toggle a bit:
- Create mask: 1 << position
- Set bit: n = n | mask
- Clear bit: n = n & ~mask
- Toggle bit: n = n ^ mask
- Bit positions start at 0 from right (LSB)

Full Transcript

This lesson shows how to change a specific bit in a number using bitwise operations. We start with a number n and a bit position p. We create a mask by shifting 1 left by p positions. To set the bit, we OR n with the mask. To clear, we AND n with the negation of the mask. To toggle, we XOR n with the mask. The example sets bit 2 of 13 (binary 1101). Since bit 2 was already set, the number stays the same. This method lets us control individual bits easily.