PHP

PHP is a server side scripting language.

Basic Syntax & Commands

PHP statements are always terminated with semicolon (;).

Single quotes are used to mark start and end of text ()

All variable names in PHP start with dollar sign ($).

PHP is a loosely typed language. Variables may contain any type of data.

Example:

$variable_name = "Semper Fidelis";

Equal sign is called the assignment operator since it assigns values to variables.

Comments begin with // or /* */

arithmetic operators enable you to add, subtract, multiply, & divide.

concatenation operator allows you to add strings of text.

Example:

$variable_name = "Hello" . " there" . " world!";

Assigns value of "Hello there world!" without quotes.

Examples:

variable	comment
$var1 = 'PHP';	Assigns value of "PHP" to var1
$var2 = 5;	Assigns value of 5 to $var2
$var3 = $var2 + 1;	Assigns value of 6 to $var3
$var2 = $var1;	Assigns value of "PHP" to $var2
echo($var1);	Outputs "PHP"
echo($var2);	Outputs "PHP"
echo($var3);	Outputs 6
echo($var1 . ' rules!');	Outputs "PHP rules!"
echo("var1 rules!");	Outputs "PHP rules!"
echo('var1 rules!');	Outputs '$var1 rules!'

NOTE: Double quotes around text enables the variable name to be inserted & value is displayed. This is called variable interpolation. Single quotes will not interpolate the variable name.

Arrays

A special variable that contains multiple values.

Simple format:

$array_name = array('test1', 'test2', 69);

To retrieve a value stored in an array you need the index.

Generally, arrays use incrementing integers that start with zero as their indices. Indices act as pointers to precisely locate a value in an array.

Expanding on simple format:

code	comment
echo($array_name[0]);	Outputs 'test1'
echo($array_name[1]);	Outputs 'test2'
echo($array_name[2]);	Outputs 69
$array_name[1] = 'wiki1';	Assign a new value
$array_name[3] = 'wiki2';	Create a new element
$array_name[] = 'transformers';	Add element to end of array.
echo($array_name[4]);	Outputs "transformers"

Arrays can use strings for indices. This is called an associative array because we can associate values with meaningful indices.

Example:

$weight['robert'] = 225;

$weight['gene'] = 180;

$weight['julie'] = 103;

Array Variables

Array variables useful to HTML

Array variable	comment
$_GET
$_POST
$_REQUEST
$_SERVER

Functions

Functions are good for your health.

function syntax	description
echo	outputs data to browser
urlencode	takes any special characters in a string (like spaces) & converts them into special codes to appear in php query strings
mysql_connect(address, username, password);	Enables connection to MySQL database, returns a number that identifies the connection that has been established
exit( );	Commands PHP to stop reading page.
blah	blah
isset	returns a value of true if the identified variable has a value
blah	blah
blah	blah
blah	blah

mysql_connect example

Example code:

$dbcnx = @mysql_connect ('db_hostname', 'db_user_name', 'db_user_password');

if (!$dbcnx) {

echo ( '<p>Unable to connect to the ' .

'database server at this time.</p>' );

exit ();

}

• The '@' symbol tells the function to fail silently which enables the coder to display your own message.
• The '!' symbol flips the $dbcnx value. A returned number for $dbcnx is true (your code successfully connected to MySQL db. !$dbcnx means a successful db connection results in false and the if statement would not execute. !$dbcnx means a failed db connection results in true and the if statement would execute (print the custom error message).

• exit() function causes php to stop reading the page

User Interaction & Forms

Formats, tips, and suggestions for user interaction & forms.

Variables can be separated in s query string by an ampersand (&). You may use the ampersand multiple times.

Web pages that can decide whether to display more than one pages is a multipurpose page.

Sample multipurpose page in the HTML body tags:

<?php if ( condition ) { ?>

HTML content to display if condition is true

<?php } else { ?>

HTML content to display if condition is false

<?php } ?>

Control Structures

if-else statement

if ( condition ) {

executed if condition is true

} else {

executed if condition false

while loop

while ( conditions ) {

statements execute if true, then repeat, until false

}

for loop

for ( initialize; condition; update ) {

statement(s) to execute repeatedly while condition is true

}

Operators

operator	meaning
and or &&	compares two conditions both must be true
or or ||	compares two and either must be true
!	negation operator or not operator, reverses a returned value from true to false or vice versa
==	equal-to operator
!=	not equal
<	less than
>	greater than
<=	less than or equal
>=	greater than or equal