PHP 笔记一（systax/variables/echo/print/Data Type）

PHP stands for "Hypertext Preprocessor" ,it is a server scripting language.

What Can PHP Do?

• PHP can generate dynamic page content
• PHP can create, open, read, write, delete, and close files on the server
• PHP can collect form data
• PHP can send and receive cookies
• PHP can add, delete, modify data in your database
• PHP can be used to control user-access
• PHP can encrypt data

1> Basic PHP Syntax

 <?php
 // PHP code goes here
 ?>

2> Comments in PHP

 <?php
 // This is a single-line comment

 # This is also a single-line comment

 /*
 This is a multiple-lines comment block
 that spans over multiple
 lines
 */

 // You can also use comments to leave out parts of a code line
 $x = 5 /* + 15 */ + 5;
 echo $x;
 ?>

3> Case Sensitivity

In PHP, all keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are NOT case-sensitive.

 <?php
 ECHO "Hello World!<br>";
 echo "Hello World!<br>";
 EcHo "Hello World!<br>";
 ?>

However; all variable names are case-sensitive.

 <?php
 $color = "red";
 echo "My car is " . $color . "<br>";
 echo "My house is " . $COLOR . "<br>";
 echo "My boat is " . $coLOR . "<br>";
 ?>

4> PHP Variables

Rules for PHP variables:

• A variable starts with the $ sign, followed by the name of the variable
• A variable name must start with a letter or the underscore character
• A variable name cannot start with a number
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Variable names are case-sensitive ($age and $AGE are two different variables)

PHP is a Loosely Typed Language

PHP Variables Scope

PHP has three different variable scopes:

• local
• global
• static

PHP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable.

 <?php
 $x = 5;
 $y = 10;

 function myTest() {
     $GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
 }

 myTest();
 echo $y; // outputs 15
 ?> 

5> PHP echo and print Statements

echo and print are more or less the same. They are both used to output data to the screen.

The differences are small:

• echo has no return value while print has a return value of 1 so it can be used in expressions.
• echo can take multiple parameters (although such usage is rare) while print can take one argument.
• echo is marginally faster than print.

echo Display Text

 <?php
 echo "<h2>PHP is Fun!</h2>";
 echo "Hello world!<br>";
 echo "I'm about to learn PHP!<br>";
 echo "This ", "string ", "was ", "made ", "with multiple parameters.";
 ?> 

echo Display Variables

 <?php
 $txt1 = "Learn PHP";
 $txt2 = "W3Schools.com";
 $x = 5;
 $y = 4;

 echo "<h2>$txt1</h2>";
 echo "Study PHP at $txt2<br>";
 echo $x + $y;
 ?> 

print Display Text

 <?php
 print "<h2>PHP is Fun!</h2>";
 print "Hello world!<br>";
 print "I'm about to learn PHP!";
 ?>

print Display Variables

 <?php
 $txt1 = "Learn PHP";
 $txt2 = "W3Schools.com";
 $x = 5;
 $y = 4;

 print "<h2>$txt1</h2>";
 print "Study PHP at $txt2<br>";
 print $x + $y;
 ?> 

6> PHP Data Types

Variables can store data of different types, and different data types can do different things.

PHP supports the following data types:

• String
• Integer
• Float (floating point numbers - also called double)
• Boolean
• Array
• Object
• NULL
• Resource

Example

 <?php
 $x = "Hello world!";
 $y = 5985;
 $z = 10.365;
 $cars = array("Volvo","BMW","Toyota");
 // var_dump() function returns the data type and value
 var_dump($cars);
8 $a = null;

Object Example

 <?php
 class Car {
     function Car() {
         $this->model = "VW";
     }
 }

 // create an object
 $herbie = new Car();

 // show object properties
 echo $herbie->model;
 ?>