Bitwise NOT in C - Step-by-Step Execution

Concept Flow - Bitwise NOT

Start with integer value

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Apply bitwise NOT (~) operator

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Flip each bit: 0->1, 1->0

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Result is new integer with flipped bits

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Use or print the result

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End

The bitwise NOT operator flips every bit of an integer, turning 0s into 1s and 1s into 0s, producing a new integer.

Execution Sample

C

int x = 5;
int y = ~x;
printf("%d", y);

This code flips all bits of 5 and prints the resulting integer.

Execution Table

Step	Variable	Value (decimal)	Value (binary 8-bit)	Operation	Result (binary)	Result (decimal)
1	x	5	00000101	Initial value	00000101	5
2	y	N/A	N/A	Apply ~x (bitwise NOT)	11111010	-6
3	y	-6	11111010	Print y	11111010	-6

💡 Program ends after printing the bitwise NOT of 5, which is -6 in two's complement.

Variable Tracker

Variable	Start	After Step 2	Final
x	5	5	5
y	undefined	-6	-6

Key Moments - 2 Insights

Why does ~5 become -6 instead of a large positive number?

Because integers use two's complement representation, flipping bits of 5 (00000101) results in 11111010, which is -6 in two's complement. See execution_table step 2.

Why do we show 8 bits in binary when integers are usually 32 bits?

For simplicity and clarity, we show 8 bits here. The actual integer has more bits, but the principle of flipping each bit is the same. The sign bit determines if the number is negative.

Visual Quiz - 3 Questions

Look at the execution_table, what is the binary result of applying ~ to 5?

A 00000101

B 11111010

C 11111101

D 00011010

💡 Hint

Check the 'Result (binary)' column in step 2 of execution_table.

At which step is the variable y assigned a value?

A Step 2

B Step 1

C Step 3

D Never

💡 Hint

Look at the 'Operation' column where ~x is applied and y gets its value.

If x was 0 instead of 5, what would be the decimal value of ~x?

A 1

B 0

C -1

D -0

💡 Hint

Remember that ~0 flips all bits to 1, which is -1 in two's complement.

Concept Snapshot

Bitwise NOT (~) flips every bit of an integer.
Example: ~5 flips 00000101 to 11111010.
In two's complement, this results in -6.
Useful for low-level bit manipulation.
Always remember sign bit affects result.

Full Transcript

The bitwise NOT operator (~) takes an integer and flips all its bits. For example, starting with 5, which is 00000101 in binary (8-bit shown for simplicity), applying ~ flips every bit to 11111010. In two's complement representation, this binary number equals -6. The program stores this result in variable y and prints it. This shows how bitwise NOT changes positive numbers into negative ones by flipping bits, including the sign bit. Understanding two's complement is key to interpreting the result correctly.