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# C Bitwise AND Assignment
The `&=` operator is the bitwise AND assignment operator in C. It performs a bitwise AND operation between the binary representations of the left and right operands, and subsequently assigns the resulting value to the left operand.
```c theme={"dark"}
lvalue &= rvalue;
```
This compound assignment operator is syntactic sugar for the following equivalent expression, with the exception that the `lvalue` is evaluated only once:
```c theme={"dark"}
lvalue = lvalue & (rvalue);
```
## Mechanics and Constraints
* **Operand Types:** Both operands must be of integral types (e.g., `char`, `short`, `int`, `long`, `unsigned` variants). The operator cannot be applied to floating-point types or pointers.
* **Evaluation Order:** The `rvalue` expression is fully evaluated before the bitwise AND operation is performed.
* **Type Promotion:** Standard integer promotion rules apply. If the operands are of different sizes or signedness, the compiler promotes them to a common type before executing the bitwise operation. The final result is then truncated or converted back to the type of the `lvalue` during assignment.
* **Bit-Level Logic:** The operator compares each bit of the left operand to the corresponding bit of the right operand. The resulting bit is set to `1` if and only if both corresponding bits are `1`. Otherwise, the resulting bit is `0`.
## Truth Table
| Left Operand Bit | Right Operand Bit | Resulting Assigned Bit |
| :--------------: | :---------------: | :--------------------: |
| `0` | `0` | `0` |
| `0` | `1` | `0` |
| `1` | `0` | `0` |
| `1` | `1` | `1` |
## Execution Example
```c theme={"dark"}
unsigned char a = 12; // Binary representation: 0000 1100
unsigned char b = 10; // Binary representation: 0000 1010
a &= b;
```
**Step-by-step evaluation:**
1. Align the binary values:
`0000 1100` (a)
`0000 1010` (b)
2. Apply bitwise AND logic per column:
`0000 1000`
3. Assign the result back to `a`. The variable `a` now holds the decimal value `8`.
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