> ## Documentation Index
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> Use this file to discover all available pages before exploring further.
# PHP Pre-Increment
The `++` operator is a unary mutating operator in PHP that increments the value of a variable by one. It directly modifies the operand in memory and evaluates to either the original or the incremented value, depending on its syntactic placement relative to the variable.
## Evaluation Modes
The operator functions in two distinct modes based on its position:
**1. Pre-increment (`++$variable`)**
The variable is incremented first, and the expression evaluates to the *new* mutated value.
```php theme={"dark"}
$x = 10;
$result = ++$x;
// $x is mutated to 11
// $result is assigned 11
```
**2. Post-increment (`$variable++`)**
The expression evaluates to the *original* value of the variable, and the variable is incremented afterward.
```php theme={"dark"}
$y = 10;
$result = $y++;
// $result is assigned 10
// $y is mutated to 11
```
## Type-Specific Behavior and Coercion
Unlike standard binary addition (`$var + 1`), the `++` operator does not strictly cast all types to integers or floats. It applies specific internal rules based on the operand's underlying `zval` type:
* **Integers and Floats:** Performs standard arithmetic incrementation.
* **Null:** Coerces the value to `1`.
* **Booleans:** The operator does not mutate the value (`true` remains `true`, and `false` remains `false`). As of PHP 8.3, applying the `++` operator to a boolean emits an `E_WARNING`.
* **Strings:** Behavior depends on the string's contents:
* *Numeric strings:* Strings containing valid numeric values (e.g., `"5"`, `"5.5"`) are coerced into `int` or `float` types and incremented arithmetically (e.g., `"5"` becomes `int(6)`).
* *Non-numeric strings:* Historically, PHP applies a Perl-style alphanumeric increment where characters carry over (e.g., `'a'` becomes `'b'`, `'Z'` becomes `'AA'`). As of PHP 8.3, applying the `++` operator to non-numeric strings is deprecated and emits an `E_DEPRECATED` notice.
* **Arrays:** Applying the `++` operator results in a `TypeError`.
* **Objects:** Applying the `++` operator to standard userland objects results in a `TypeError`. However, internal classes that support operator overloading at the engine level (such as `GMP` objects) can be successfully incremented.
## Internal Execution
At the compilation level, the Zend Engine translates the `++` operator into specific opcodes (`ZEND_PRE_INC` or `ZEND_POST_INC`). Because these opcodes are designed to mutate a variable's `zval` directly in place, the `++` operator requires a memory reference. It is strictly bound to variables and cannot be applied to literal values or expressions.
```php theme={"dark"}
// Valid: Applied to a variable reference
$a = 5;
$a++;
// Valid: Applied to an internal object supporting operator overloading
$gmp = gmp_init(5);
$gmp++;
// Invalid: Parse error: syntax error, unexpected integer "5", expecting variable
++5;
// Invalid: Parse error: syntax error, unexpected token "++"
(2 + 3)++;
// Invalid: Fatal error: Cannot use temporary expression in write context
[1, 2, 3][0]++;
```
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