PHP basics - constants - basic functions related to variables_PHP tutorial

php basics-constants-variable related basic functions

Comment statement


//Single line


# Single line


/*
Multi-line comments
*/


/**
* Documentation comments
*
*/


Constant definition


Custom constants constant names are case-sensitive
The system's magic constants are not case-sensitive __DIR__ __dir__




Variable definition
Variable names are case sensitive
When declaring a variable name, start with the $ symbol and comply with the naming rules for variable names






$i;
var_dump($i);


$i = 'ok';
var_dump($i);




$i = "Hello";
var_dump($i);




$i = 20;
var_dump($i);




$i = 20.5;
var_dump($i);


//Variable type is similar to javascript variable type, it is a variant type
$i = true;
var_dump($i);






Function name, class name, case-insensitive






PHP basic functions


phpinfo();
var_dump($i);
echo gettype($i);
define('AGE',200);
defined('AGE');


realpath()
dirname();