Introduction to PHP

A user navigates in her browser to a page that ends with a .php extension

The request is sent to a web server, which directs the request to the PHP interpreter

The PHP interpreter processes the page, communicating with file systems, databases, and email servers as necessary

Finally delivers a web page to the web server, which is served to the browser

Syntax

PHP code can be inserted into HTML files using a special set of tagsStandard tags

<?php. . . code?>

Short tags<?. . . code?><? =$variable ?>

Script tags<script language=“php”>. . . code</script>

ASP tags<%. . . code%>asp_tags in php.ini

Short, script and ASP tags are considered deprecatedand their usage is stronglydiscouraged

Comments

PHP comments Commenting is important in any

programming language to document the behaviour of the code. Otherwise maintenance becomes difficult.

Supports C, C++ and Unix shell style (Perl style) comments

//one line C++ style comment

/* this is a multi-line comment. Yet another line of comment */

# one line shell style comment

d1comments.php source

d1comments.php

Datatypes [1]

Various types of datatypes in PHP

Scalar Contains only one value at a time PHP supports four scalar datatypes boolean int float string

Compound array object

Special types resource null

Datatypes [2]

Scalar data types

Numeric values integer

Used to represent signed integers Can use decimal, octal and

hexadecimal notations Start with 0 for octal (base 8) and 0x

for hexadecimal (base 16) notation float

Are numbers that have a fractional component

Two different notations to express them

Decimal (e.g. 0.12, 1234.43) Exponential (e.g. 2E7, 1.2e2)

String Series of characters within PHP, each character is

represented by a single byte Upto PHP 5, no support for multi-

byte character sets PHP does not impose any limit on

length of strings 3 ways of string output

Boolean They hold only one of two possible

values true or false Any integer other than 0 is cast to

TRUE TRUE & FALSE are case

insensitive, though the all capitals representation is widely used

Datatypes [3]

Compound Essentially container(s) for multiple

data elements / data and code Array

Containers of multiple ordered data elements

Can be used to store and retrieve any other data type, including numbers, boolean values, strings, objects and even arrays

Covered in more detail in a subsequent section

Object Objects are containers of data

and code They allow a cohesive

combination of data and code They are the fundamental

blocks of OOP (Object Oriented Programming)

Datatypes [4]

Special datatypes

Null A null variable is special, as it has

no type and no value NULL is not the same as integer

zero nor the zero length string (both have types)

A variable is considered NULL if it is assigned the constant NULL, or it is not set to any value as yet or it has been unset (using unset()).

Resource Resources are special

variables. They hold references to

external resources (some sort of operating system resource such as an open file or database connection)

Resources are created by using special functions, depending on the type of the resource

Functions is_resource() and get_resource_type() are commonly used with resources

Constants & variables

Constants Are identifiers for immutable

values (viz., the value cannot be changed in the course of execution of the script)

Constants are created using the define() function and are by convention all in uppercase letters

Constants can be accessed from anywhere on the page

No need to use $ in front of the constant name, as in the case of a variable

Variables Are temporary storage

containers In PHP, a variable can contain

any type of data. PHP is loosely typed, meaning it will change the type of a variable as needed

Variables are identified by $ sign, followed by an identifier name

isset() is used to determine whether a variable exists or not

Other relevant functions are unset() and empty()

d1datatype.php source d1datatype.php

Operators

Assignment For assigning data to variables

(assignment with operation as well)

Arithmetic For performing basic

mathematic functions

String For joining two or more strings

Comparison For comparing two values (i.e.

pieces of data). Various rules govern the comparison process

Logical For performing logical

operations on boolean values

Bit-wise For manipulating bits using

boolean algebra

Error control For suppressing errors

Execution For executing system

commands

Increment / Decrement For incrementing /

decrementing numeric values

Type For identifying operators

d1operator.php sourced1operator.php

Control structures

If Normal, alternate, short

switch

while

do-while

for continue break

foreach

return

require

Include

d1controlstruct.php source

d1controlstruct.php

if statement

conditionalIf (expression)true_statement;elsefalse_statement;

if (expression1) {} elseif (expression2) {// Note that the space

between else and if is optional

} else {}

alternate syntaxopening brace { = :closing brace } = endif;if (expression1):statements;elseif (expression2):statements;endif;Ternary conditional

operator$variable = (expression) ?

true_expression: false_expression;