Intro to PHP Operators

Definition

In PHP, operators are symbols or keywords that perform specific operations on one or more operands. Operators include mathematical operators (+, -, *, /, %), comparison operators (==, !=, >, <, >=, <=), logical operators (&&, ||, !), and more. They are used to manipulate and compare values in PHP scripts, and can be used to control the flow of a program. There are several types of operators available in PHP, including:

Understanding Operator Precedence and Associativity

Before diving into specific operators, it's crucial to understand how PHP evaluates expressions with multiple operators. Operator precedence determines which operations are performed first, while associativity determines the order when operators have the same precedence.

Key Concepts:

Precedence: Higher precedence operators are evaluated first
Associativity: Left-to-right or right-to-left evaluation for same precedence
Parentheses: Always override default precedence
Type Juggling: PHP may convert operand types automatically

Arithmetic operators: These operators are used to perform mathematical operations such as addition, subtraction, multiplication, division, and modulus.
Arithmetic Operations in Detail:
- Addition (+): Adds numeric values or converts strings to numbers
- Subtraction (-): Subtracts values; also serves as unary negation
- Multiplication (*): Multiplies values with automatic type conversion
- Division (/): Always returns float unless both operands are integers that divide evenly
- Modulus (%): Returns remainder; converts operands to integers first
- Exponentiation ()**: Power operator (PHP 5.6+)
Comparison operators: These operators are used to compare values and determine if they are equal, greater than, less than, or not equal.
Comparison Nuances:
- Loose vs Strict: == allows type juggling, === requires identical types
- Spaceship Operator (<=>): Three-way comparison returning -1, 0, or 1 (PHP 7+)
- Type Coercion: Understanding how PHP converts types during comparisons
- String Comparisons: Lexicographic when both operands are strings
- Null Coalescing (??): Returns first non-null value (PHP 7+)
Logical operators: These operators are used to combine multiple conditions and determine if they are true or false.
Logical Operation Behaviors:
- Short-Circuit Evaluation: && and || stop evaluating when result is determined
- Alternative Syntax: and, or, xor have lower precedence than &&, ||
- Boolean Context: Non-boolean values are converted to boolean
- XOR Operator: True when exactly one operand is true
Assignment operators: These operators are used to assign values to variables.
Assignment Variations:
- Simple Assignment (=): Basic value assignment
- Compound Assignment (+=, -=, etc.): Combines operation with assignment
- Reference Assignment (&=): Creates reference instead of copy
- Array Operators: += for arrays performs union, not addition
- Null Coalescing Assignment (??=): Assigns only if variable is null (PHP 7.4+)
Increment/Decrement operators: These operators are used to increase or decrease the value of a variable by a certain amount.
Pre vs Post Increment/Decrement:
- Pre-increment (++$x): Increments then returns new value
- Post-increment ($x++): Returns current value then increments
- String Increment: PHP can increment strings ('Z' becomes 'AA')
- No String Decrement: Decrement doesn't work on strings
Conditional operators: These operators are used to perform different actions depending on a certain condition.
Ternary and Elvis Operators:
- Ternary (?:): Inline if-else expression
- Elvis Operator (?:): Shorthand when true expression equals condition
- Null Coalescing (??): Specifically checks for null, not falsy
- Chaining: Multiple operators can be chained but reduce readability

Here are a few examples of different types of operators used in PHP:

Mathematical Operators:

$x = 10;
$y = 5;
$sum = $x + $y; // $sum = 15
$diff = $x - $y; // $diff = 5
$product = $x * $y; // $product = 50
$quotient = $x / $y; // $quotient = 2
$remainder = $x % $y; // $remainder = 0

Mathematical Operations Explained:

Each operation has specific behaviors worth understanding:

Addition (+):

Converts strings to numbers: "10" + "5" equals 15
Non-numeric strings become 0: "hello" + 5 equals 5
Arrays cannot be added (causes fatal error)
Floating point precision issues: 0.1 + 0.2 might not equal 0.3 exactly

Division (/):

Always returns float unless both operands are integers that divide evenly
Division by zero triggers warning and returns INF or -INF
Use intdiv() function for integer division (PHP 7+)
Example: 10 / 3 returns 3.3333..., intdiv(10, 3) returns 3

Modulus (%):

Operands are converted to integers before operation
Result has same sign as dividend (first operand)
Useful for: checking even/odd, cycling through values, time calculations
Example: -10 % 3 equals -1, not 2

Comparison Operators:

$x = 10;
$y = 5;
$result = ($x == $y); // $result = false
$result = ($x != $y); // $result = true
$result = ($x > $y); // $result = true
$result = ($x < $y); // $result = false
$result = ($x >= $y); // $result = true
$result = ($x <= $y); // $result = false

Understanding Comparison Results:

PHP's comparison operators exhibit important behaviors:

Type Juggling in Comparisons:

"10" == 10 is true (string converted to number)
"10" === 10 is false (different types)
0 == "php" is true (non-numeric string converts to 0)
null == false is true, but null === false is false

Special Comparison Cases:

// Comparing different types
var_dump(0 == "0");     // true
var_dump(0 === "0");    // false
var_dump(null == "");   // true
var_dump(null === "");  // false

// Array comparisons
$arr1 = [1, 2, 3];
$arr2 = [1, 2, 3];
var_dump($arr1 == $arr2);  // true (same values)
var_dump($arr1 === $arr2); // true (same values and order)

// Object comparisons
$obj1 = new stdClass();
$obj2 = new stdClass();
var_dump($obj1 == $obj2);  // true (same properties)
var_dump($obj1 === $obj2); // false (different instances)

Logical Operators:

$x = true;
$y = false;
$result = ($x && $y); // $result = false
$result = ($x || $y); // $result = true
$result = !$x; // $result = false

Logical Operator Behaviors:

Short-Circuit Evaluation:

// Second condition not evaluated if first is false
$result = false && expensiveFunction(); // expensiveFunction() never called

// Second condition not evaluated if first is true  
$result = true || expensiveFunction(); // expensiveFunction() never called

// Practical use
$user = isset($_SESSION['user']) && $_SESSION['user']->isActive();

Precedence Differences:

// && has higher precedence than ||
$result = true || false && false; // true (evaluated as true || (false && false))

// 'and' and 'or' have lower precedence than assignment
$result = true or false; // $result is true (assignment happens first)
$result = (true or false); // $result is true (parentheses change precedence)

Assignment Operators:

$x = 10;
$x += 5; // $x = 15
$x -= 5; // $x = 10
$x *= 2; // $x = 20
$x /= 2; // $x = 10
$x %= 3; // $x = 1

Compound Assignment Benefits:

Compound operators offer more than just shorter syntax:

Efficiency: Variable is evaluated only once

$array[$complexCalculation()] += 10; // complexCalculation() called once
// vs
$array[$complexCalculation()] = $array[$complexCalculation()] + 10; // called twice

Array Union Operator:

$arr1 = [1, 2, 3];
$arr2 = [3, 4, 5, 6];
$arr1 += $arr2; // [1, 2, 3, 6] - preserves keys, doesn't re-index

String Concatenation Assignment:

$message = "Hello";
$message .= " World"; // $message = "Hello World"

String Operators:

$x = "String ";
$y = "Message";
$result = $x . $y; // $result = "String Message"

String Operation Details:

Concatenation Operator (.):

Converts non-strings to strings automatically
Different from addition: "2" . "3" equals "23", not 5
Can chain multiple concatenations: $a . $b . $c
Performance tip: For many concatenations, consider using array implode

Concatenation Assignment (.=):

$html = '<div>';
$html .= '<p>Content</p>';
$html .= '</div>';
// More efficient than repeated concatenation for building strings

Operators are essential for various types of operations in PHP, and it's important to use them correctly and understand their behavior to be able to write efficient and effective code.

Additional Operator Types

Bitwise Operators

Bitwise operators work on the binary representation of numbers:

$a = 5;  // 101 in binary
$b = 3;  // 011 in binary

$and = $a & $b;  // 001 = 1 (AND)
$or = $a | $b;   // 111 = 7 (OR)
$xor = $a ^ $b;  // 110 = 6 (XOR)
$not = ~$a;      // ...11111010 = -6 (NOT)
$left = $a << 1; // 1010 = 10 (left shift)
$right = $a >> 1; // 10 = 2 (right shift)

Common Bitwise Use Cases:

Permission systems (flags)
Network programming (IP addresses)
Performance optimizations
Cryptographic operations

Type Operators

// instanceof operator
if ($object instanceof MyClass) {
    // Object is instance of MyClass
}

// Type casting operators
$int = (int) "123";      // 123
$float = (float) "3.14"; // 3.14
$string = (string) 123;  // "123"
$bool = (bool) "false";  // true (non-empty string)
$array = (array) $object; // Convert object to array

Error Control Operator

// @ suppresses error messages
$result = @file_get_contents('nonexistent.txt'); // No warning displayed

// Better approach: proper error handling
if (file_exists('file.txt')) {
    $result = file_get_contents('file.txt');
}

Warning: The @ operator should be used sparingly as it makes debugging difficult and can hide important errors.

Best Practices

To make it easy to understand which variable is being used and for what purpose, it is important to use clear and descriptive variable names.
Good variable names make operator usage clearer: $totalPrice = $basePrice + $tax is more readable than $t = $b + $x. This becomes especially important in complex expressions.
Use parentheses to group expressions and ensure that the order of operations is clear.
Even when not strictly necessary, parentheses improve readability: $result = ($a + $b) * $c is clearer than relying on precedence rules. This prevents bugs and makes intent explicit.
Make sure to use the correct operator for the task at hand. For example, use the equality operator (==) for comparisons and the assignment operator (=) for assignments.
Common mistake: Using = in conditionals: if ($x = 5) always evaluates to true and assigns 5 to $x. Use if ($x == 5) or better yet if ($x === 5) for comparison.
Instead of using multiple assignments in one statement, use separate statements to make the code more readable.
Avoid: $a = $b = $c = 0; While valid, it's less clear than separate assignments. Each statement should have one clear purpose.
The ternary operator can make code more concise, but it can also make it more difficult to read. Use it sparingly and only when it makes the code more readable.
Good: $status = $isActive ? 'Active' : 'Inactive'; Bad: Nested ternaries that require mental parsing. Use if-else for complex logic.
Be aware of the way that PHP handles type juggling and make sure that your code is doing what you expect it to do.
Always validate and sanitize input. Use strict comparisons when type matters. Be especially careful with user input that might be strings but represent numbers.
Avoid using the increment/decrement operators as part of a larger expression: These operators can be hard to spot in a larger expression, which can make code more difficult to read and understand.
Confusing: $array[$i++] = $value++; Clear: Separate the operations for better readability.
Whether you prefer to use the short-hand notation for operators or the long notation, be consistent throughout your code.
Pick either &&/|| or and/or and stick with it. Mixing styles confuses readers and can cause precedence-related bugs.
Make sure to use parentheses to group expressions and ensure that the order of operations is clear.
Complex expressions should be broken down or parenthesized. Reader shouldn't need to memorize precedence tables.
Due to the way that floating point numbers are represented in computers, using the modulus operator with floating point numbers can lead to unexpected results.
For float comparisons, use epsilon comparison. For modulus with floats, consider using fmod() function instead. Always be aware of floating-point precision limitations.

Introduction to PHP Operators

Definition

Understanding Operator Precedence and Associativity

Mathematical Operators:

Comparison Operators:

Logical Operators:

Assignment Operators:

String Operators:

Additional Operator Types

Bitwise Operators

Type Operators

Error Control Operator

Best Practices

On this page

Definition

Additional Operator Types

Best Practices