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

Concept Flow - Set Clear Toggle a Specific Bit

Start with number

↓

Choose bit position

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Select operation: Set / Clear / Toggle

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Create mask with 1 shifted to bit position

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Apply operation using bitwise operator

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Update number with new bit value

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Result: number with bit changed

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

Execution Sample

DSA C

int num = 13; // binary 1101
int pos = 1; // bit position (0-based)
// Set bit
num = num | (1 << pos);

This code sets the bit at position 1 of number 13 (binary 1101).

Execution Table

Step	Operation	Number (decimal)	Number (binary)	Mask (binary)	Bitwise Operation	Result (decimal)	Result (binary)
1	Start	13	1101	-	-	13	1101
2	Create mask	-	-	0010	-	-	-
3	Set bit	13	1101	0010	1101 OR 0010	15	1111
4	Clear bit	15	1111	0010	1111 AND NOT 0010	13	1101
5	Toggle bit	13	1101	0010	1101 XOR 0010	15	1111
6	Toggle bit again	15	1111	0010	1111 XOR 0010	13	1101
7	End	13	1101	-	-	-	-

💡 All operations complete; bit at position 1 has been set, cleared, and toggled as shown.

Variable Tracker

Variable	Start	After Set	After Clear	After Toggle 1	After Toggle 2	Final
num	13 (1101)	15 (1111)	13 (1101)	15 (1111)	13 (1101)	13 (1101)
pos	1	1	1	1	1	1
mask	-	2 (0010)	2 (0010)	2 (0010)	2 (0010)	2 (0010)

Key Moments - 3 Insights

Why do we use (1 << pos) to create the mask?

Because shifting 1 left by pos moves the single 1 bit to the correct position to target that bit. See execution_table step 2 where mask is 0010 for pos=1.

Why does clearing a bit use AND with NOT mask?

AND with NOT mask turns the target bit to 0 while keeping others unchanged. See execution_table step 4 where 1111 AND NOT 0010 results in 1101.

How does toggling a bit work with XOR?

XOR flips the bit if mask bit is 1, else leaves it. See steps 5 and 6 where toggling flips bit 1 between 1 and 0.

Visual Quiz - 3 Questions

Look at the execution_table, what is the decimal value of num after setting bit at position 1?

A 13

B 15

C 14

D 12

💡 Hint

Check execution_table row 3 under Result (decimal).

At which step does the bit at position 1 get cleared?

A Step 4

B Step 3

C Step 5

D Step 6

💡 Hint

Look for 'Clear bit' operation in execution_table.

If pos was 2 instead of 1, what would the mask binary be at step 2?

A 0001

B 0010

C 0100

D 1000

💡 Hint

Mask is 1 shifted left by pos bits; for pos=2, mask is 0100.

Concept Snapshot

Set, Clear, Toggle a bit:
- Create mask: 1 << pos
- Set bit: num | mask
- Clear bit: num & ~mask
- Toggle bit: num ^ mask
Bit positions start at 0 (rightmost bit).
Use bitwise ops to change only target bit.

Full Transcript

This concept shows how to change a specific bit in a number using bitwise operations. We create a mask by shifting 1 left by the bit position. To set a bit, we OR the number with the mask. To clear a bit, we AND the number with the NOT of the mask. To toggle a bit, we XOR the number with the mask. The execution table traces these steps on number 13 (binary 1101) at bit position 1, showing how the number changes after each operation.