PHP Data types and scope of variables

1) PHP supports basic data types as shown below:

An integer (integer), float (floating-point), String (String), Boolean (Boolean), Array (array), object, and two special types: null (empty), resource (Resource).

Note: A variable that is not assigned, has been reset, or is assigned a special value of NULL is a variable of type null.

A specific built-in function, such as a database function, returns a variable of type resource.

2) Scopes are scopes that a variable can use or be visible in a script. PHP has 6 basic scope rules:

2.1) built-in super global variables can be used and visible anywhere in the script;

2.2) constants, once declared, will be visible globally;

2.3) The global variables declared in a script are visible throughout the script;

2.4) When a variable used inside a function is declared as a global variable, its name is the same as the global variable name;

2.5) A variable that is created inside a function and declared as static cannot be visible outside the function, but can be persisted during multiple executions of the function;

2.6) variables created inside the function are local to the function, and when the function terminates, the variable does not exist.

Note: The complete list of super global variables is as follows:

$GLOBALS--All global variable arrays;

$_server--server environment variable array;

$_get--the array of variables passed to the script by the GET method;

$_post--the array of variables passed to the script via the POST method;

An array of $_cookie--cookie variables;

$_files--array of variables related to file uploads;

An array of $_env--environment variables;

$_request--the array of variables entered by all users, including the input contained in $_get, $_post, and $_cookie;

An array of $_session--session variables.

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PHP Data types and scope of variables