Learn PHP
PHP Language Basics
    General
  • When a PHP file only contains PHP code then we do not need closing tag of PHP ?>
  • PHP prints white spaces (you can see in the Page Source), but HTML ignores/removes that white space.
    Variables
  • Variable declaration require to start variable with $ sign followed by a character.
  • We cannot use - + % for the variable name. However can use underscores. i.e. $first_name
  • Variables are case sensative.
  • There is no need to initialize the variable as it all happens at the declaration time. i.e. $first_name = "Jhon"
  • A variable can hold any type of data i.e. string to integer and vice versa.
  • Superglobals are built-in/predefined variables, always available in all of the scopes. (See documentation of Superglobals And Predefined Variables)
    Constants
  • Constant is the value that does not change.
  • We cannot use isset() for constant. This is only to check if a variable is set/defined or not.
  • Once constant is defined, the original value cannot be changed even if we reassign another value after defining it.
  • Constant scope is global within a page/program.
    Data Types
  • SCALAR Data Type: These are the data types that hold single value.
  • There are four SCALAR data types. Boolean, Integer, Float and String.
  • SCALAR means it holds single value, unlike arrays, hash table, link table and class
    Case Sensitivity
  • Not everything is case sensative. We can write echo/Echo/ECHO, print/Print/PRINT and <?PHP but variables are case sensatives.
    • The function names are also not case sensative. Greetings(); GREETINGS(); both will work regardless how it was defined.
    • However we cannot define two functions with same name but different cases. i.e.
      function Greetings() and function GREETINGS() will NOT work and we will get error.
    Include and Require
  • include() does not stop the execution of the rest of the page if file is not found which is included.
  • require() stops the execution of the rest of the page if file is not found which is required.
  • include_once() and require_once() only include the files once even if we try to include same file multiple times.

    • With the following example the menu.php will only be added once even it is being included twice. include_once(“menu.php ”)

    However in the following example it will be added twice.

    include_once(“menu.php ”) include(“menu.php ”)