> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntblaze.com/llms.txt
> Use this file to discover all available pages before exploring further.
# C Bitwise OR
The `|` operator in C is the bitwise inclusive OR operator. It performs a logical disjunction on each pair of corresponding bits of two integral operands. If either or both bits in the compared position are `1`, the resulting bit is `1`; if both bits are `0`, the resulting bit is `0`.
```c theme={"dark"}
result = operand1 | operand2;
```
## Truth Table
The operator evaluates operands at the binary level according to the following truth table:
\| Bit A | Bit B | A `|` B |
\| :---: | :---: | :---: |
\| 0 | 0 | **0** |
\| 0 | 1 | **1** |
\| 1 | 0 | **1** |
\| 1 | 1 | **1** |
## Operand Constraints
The `|` operator strictly requires operands of integral types (e.g., `char`, `short`, `int`, `long`, `unsigned` variants, and `_Bool`). Attempting to use the `|` operator with floating-point types (`float`, `double`) or pointer types will result in a compilation error.
## Integer Promotion and Type Conversion
Before the bitwise OR operation is executed, C applies standard integer promotions to the operands:
1. If the operands are of types smaller than `int` (such as `char` or `short`), they are promoted to `int` or `unsigned int`.
2. If the operands are of different types, the compiler applies the usual arithmetic conversions to establish a common type.
3. The operation is then performed, and the resulting value shares this common promoted type.
## Evaluation Mechanics
When evaluating `a | b`, the compiler aligns the bit sequences of both operands and applies the OR logic vertically to each bit index.
```c theme={"dark"}
unsigned char a = 10; // Binary: 0000 1010
unsigned char b = 12; // Binary: 0000 1100
unsigned char c = a | b;
/*
Evaluation:
0000 1010 (10)
| 0000 1100 (12)
0000 1110 (14)
*/
```
## Compound Assignment
The bitwise OR operator can be combined with the assignment operator to form the compound assignment operator `|=`. This mutates the left operand by applying the bitwise OR operation between it and the right operand.
```c theme={"dark"}
operand1 |= operand2;
// Semantically equivalent to: operand1 = operand1 | operand2;
```
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