How to Use Bitwise NOT Operator in C: Syntax and Examples

In C, the bitwise NOT operator is ~. It flips every bit of an integer value, turning 0s into 1s and 1s into 0s. Use it by placing ~ before an integer variable or value, like ~x.

Syntax

The bitwise NOT operator in C is a unary operator represented by ~. It takes one integer operand and returns the bitwise complement of that operand.

• ~operand: Flips all bits of operand.
• operand must be an integer type (int, char, long, etc.).

c

~x

Example

This example shows how ~ flips bits of an integer. It prints the original number and its bitwise NOT result.

c

#include <stdio.h>

int main() {
    unsigned int x = 5; // binary: 00000000 00000000 00000000 00000101
    unsigned int result = ~x;

    printf("Original x: %u\n", x);
    printf("Bitwise NOT ~x: %u\n", result);

    return 0;
}

Output

Original x: 5
Bitwise NOT ~x: 4294967290

Common Pitfalls

Common mistakes when using ~ include:

• Using signed integers without understanding two's complement representation, which can cause unexpected negative results.
• Confusing bitwise NOT ~ with logical NOT !.
• Not considering the size of the integer type, which affects the number of bits flipped.

Always use unsigned types if you want predictable bit-flipping results.

c

#include <stdio.h>

int main() {
    int x = 5;
    int wrong = !x;  // Logical NOT, not bitwise
    int right = ~x;   // Bitwise NOT

    printf("Logical NOT !x: %d\n", wrong);
    printf("Bitwise NOT ~x: %d\n", right);

    return 0;
}

Output

Logical NOT !x: 0
Bitwise NOT ~x: -6

Quick Reference

Operator	Description	Example	Result
~	Bitwise NOT (flips bits)	~5	Depends on int size, e.g. -6 for signed int
!	Logical NOT (true/false)	!5	0 (false)
&	Bitwise AND	5 & 3	1
|	Bitwise OR	5 | 3	7
^	Bitwise XOR	5 ^ 3	6

Key Takeaways

Use the ~ operator to flip all bits of an integer in C.

Prefer unsigned integers with ~ for predictable results.

Do not confuse bitwise NOT (~) with logical NOT (!).

The result depends on the integer size and signedness.

Print results carefully to understand bitwise operations.