Introduction to the PHP Foundation section notes

Lamp's Overview
linux= operating system apache= foreign server mysql= database php= Run script program for the backend server
Lamp is an abbreviation for a group of Open-source software that is often used to build dynamic Web sites or servers, including: Linux operating systems, Apache Web servers, MySQL databases, PHP, Perl, or Python programming languages.

In the PHP program to write the output of things before the echo "";
Br= Line (just add one to the back of the colon)
Center= Center
H1 to h6 are all = headings

Where to add a semicolon in PHP, where you do not need to add a semicolon
There are only two programs in PHP: The structure definition statement [must not be semicolon] function execution statement [must have a semicolon]
In PHP//for Single-line comments, starting with///ending as multiple-line comment
annotation function: 1 written code do not immediately delete (in case of regret) 2 Debugger 3 Write Help document

PHP Variables and constants
Variables: variables are case-sensitive. Other no distinction
Four scalar types (boolean, Integer, floating-point, string)
Two types of composite (arrays, objects)
Two special types (resources, NULL)
Constant
1. Constants can contain only scalar data (boolean,integer,float,string)
2, can only be assigned at the time of declaration, and can not be changed at run time.
The function to check whether a variable exists is isset (); , the function to check whether the constants exist is defined ();

Operator
Arithmetic operator +-*/% + +-
comparison operator = = = = = = =!= <> <= >=? :
Logical Operators && | | ! And OR XOR
Bitwise Operators & | ^ ~ << >> >>>
Assignment operator + = = *=/=%=
Other operators. .=