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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsPHP variables begin with $, need no declaration, and take their type from the value assigned. Their behavior still depends on context: a function has its own local variables, and request variables such as $_GET contain external data that must be checked before use.
How to write a PHP variable
Put a dollar sign before a variable name, then assign it with =:
<?php
$name = 'Ada';
$count = 3;Names are case-sensitive: $name and $Name are different variables. A name starts with a letter or underscore and continues with letters, digits, or underscores. For portable beginner code, use ordinary ASCII letters, digits, and underscores rather than non-ASCII characters in names. See the PHP manual’s variable basics.
Assignment copies a value by default. A reference assignment using & is a distinct feature: the two names can then affect the same referenced variable. References are not needed for ordinary assignments, so use them only when shared-variable behavior is intentional.
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How PHP determines a variable’s type
PHP does not require a declaration that specifies a variable’s type. The assigned value determines its current type, and a later assignment can change it:
<?php
$value = '3'; // string
$value = 3; // integerPHP may convert values in some operation contexts, but conversion is not universal. The result depends on the operation and PHP version; since PHP 8.0.0, some values that cannot be interpreted for an operation cause a TypeError. Use a cast when a conversion is deliberate, or a type declaration where a function’s inputs or outputs need explicit constraints. Consult the version-specific type-juggling documentation before relying on particular conversion behavior.
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Why a variable may be unavailable inside a function
Variables created inside a function are local to it. A function does not automatically inherit a same-named variable from the global scope:
<?php
$message = 'outside';
function showMessage(): void {
// $message is not automatically available here
}
function greet(string $message): void {
echo $message;
}
greet('Hello');For routine data flow, pass values through parameters and return values. To explicitly access a global variable, PHP also provides global and the $GLOBALS array:
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<?php
$message = 'outside';
function showGlobalMessage(): void {
global $message;
echo $message;
}global $message; binds the function’s local name to the global variable; $GLOBALS['message'] is the array-based alternative. Code brought in with include runs in the scope where the include occurs. More detail is in the manual’s variable scope reference.
What superglobals such as $_GET and $_POST mean
Superglobals are predefined arrays available in every scope. Common examples include:
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$GLOBALS: variables in the global scope.$_SERVER: server and request environment information.$_GET: values supplied in the URL query string.$_POST: form data sent in an HTTP POST request.$_FILES: uploaded-file information.$_SESSION: session data.$_ENV: environment values.$_COOKIE: cookie values sent with the request.
A query parameter can be read with a fallback for the case where it is absent:
<?php
$search = $_GET['q'] ?? '';The fallback avoids assuming that q exists; it does not validate the value or make it safe. Treat request and environment values as external input: validate them for the expected use, and escape data when inserting it into HTML output. The PHP manual lists these and other predefined variables.
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What happens when you use an undefined variable
In current PHP documentation, accessing an undefined variable produces an E_WARNING; before PHP 8.0.0 it produced an E_NOTICE. The value is null by default, but depending on that implicit behavior can hide mistakes. Initialize variables deliberately, or use checks such as isset() when a value may genuinely be absent. See the manual’s variable basics and scope reference.
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