> ## 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.
# PHP Unary Minus
The `-` operator in PHP functions as both a binary arithmetic operator for subtraction and a unary arithmetic operator for arithmetic negation, depending on its arity within an expression.
## Binary Subtraction
When used with two operands, the `-` operator calculates the difference between the left operand and the right operand.
```php theme={"dark"}
$result = $expression1 - $expression2;
```
**Type Resolution:**
* Returns an `int` if both operands evaluate to integers and the resulting value does not exceed the platform's integer bounds (`PHP_INT_MAX` or `PHP_INT_MIN`).
* Returns a `float` if either operand is a float, or if the resulting integer difference causes an overflow or underflow.
## Unary Negation
When prepended to a single operand, the `-` operator acts as a unary operator that inverts the algebraic sign of the value.
```php theme={"dark"}
$result = -$expression;
```
**Type Resolution:**
* The operation generally preserves the numeric type (`int` or `float`) of the operand.
* **Exception:** Negating the minimum representable integer (`PHP_INT_MIN`) results in a `float`. Because the absolute value of `PHP_INT_MIN` is one greater than `PHP_INT_MAX`, the operation causes an integer overflow.
## Type Coercion and Juggling
PHP enforces strict type evaluation rules when applying the `-` operator to non-numeric scalar types:
* **Numeric Strings:** Strings containing valid numeric representations (e.g., `"42"`, `"-3.14"`, `"1.2e3"`) are automatically cast to their corresponding `int` or `float` values before the operation.
* **Non-Numeric Strings:** In PHP 8.0 and later, applying the `-` operator to a non-numeric string or a string with trailing non-numeric characters (e.g., `"10 apples"`) throws a `TypeError`.
* **Booleans:** `true` is coerced to the integer `1`, and `false` is coerced to the integer `0`.
* **Null:** `null` is coerced to the integer `0`.
* **Arrays and Objects:** Attempting to use the `-` operator on arrays or standard objects throws a `TypeError`.
```php theme={"dark"}
$a = 10 - "5"; // int(5)
$b = 10 - true; // int(9)
$c = 10 - null; // int(10)
$d = -"3.14"; // float(-3.14)
$e = -PHP_INT_MIN; // float(...) due to overflow
```
## Precedence and Associativity
The PHP parser handles the `-` operator differently based on its context:
* **Unary `-`:** Shares the exact same precedence level as increment/decrement operators (`++`, `--`) and type casts (e.g., `(int)`, `(float)`). It evaluates with **right-to-left** associativity.
* **Binary `-`:** Shares precedence with addition (`+`). It sits below multiplication, division, and modulo (`*`, `/`, `%`), and, as of PHP 8.0, sits strictly above the string concatenation operator (`.`). It evaluates with **left-to-right** associativity.
```php theme={"dark"}
// Left-to-right associativity for binary subtraction
$result = 10 - 5 - 2; // Evaluates as (10 - 5) - 2, resulting in int(3)
// Unary precedence
$result = 5 * -3; // Evaluates as 5 * (-3), resulting in int(-15)
```
Tired of Poor PHP Skills? Fix That With Deep Grasping!
Learn More
