PHP

PHP is a server side scripting language.

My notes originate from the book Build Your Own Database Driven Website Using PHP & MySQL by Kevin Yank 2nd Edition

For MySQL information.

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.

Constructs

Foreach loop

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	Enables connection to MySQL database, returns a number that identifies the connection that has been established
mysql_select_db	Selects database table that PHP will use.
mysql_query	Enables PHP to send MySQL queries to MySQL db
exit( );	Commands PHP to stop reading page.
mysql_affected_rows	Returns number of rows affected for DELETE, INSERT, and UPDATE queries. MySQL tracks the number of rows that were affected.
isset	returns a value of true if the identified variable has a value
mysql_fetch_array	Accepts a result as a parameter and returns the next row in the result set as an array. No row returns a false.
CURDATE()	returns current date
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

mysql_select_db example

After your code successfully connects to the MySQL db you must tell PHP which db table to use.

Example basic code:

mysql_select_db ('db_name', $dbcnx );

• The function contains the db identifier $dbcnx. This parameter is optional but I will use it for completeness. The function will default to the last connection opened.
• Function returns true when it's successful and false if an error occurs.

Example basic code with error handling:

if (! @mysql_select_db('db_name', $dbcnx) ) {
die ( '<p>Unable to locate the db_name ' .
'database at this time.</p>' );
}

• die function works like echo except the script exits after
• Executing die is equivalent to echo followed by exit

mysql_query example

Example code:

mysql_query ( query, connection_id ) ;

• query is a string that contains the SQL command we want to execute
• connection_id is optional parameter
• Returns true (success) or false (failure) for most SQL queries. SELECT queries view data in db so it requires more than true or false.
• With SELECT query mysql_query returns a number that identifies a result set which contains a list of all the rows (entries) returned from the query.
• False is always returned if query fails.

More example code:

$result = @mysql_query ('SELECT column_name0, column_name1, ... FROM table_name');

if ( !$result )  {

die ('<p>Error performing query: ' . mysql_error() .

'</p>');
}

Regular Expressions

A regular expression is a string of text that contains special codes. Enables use of a few PHP functions to search and manipulate other strings of text.

ereg - searches text for string match & is case sensitive.

eregi - like ereg except is not case sensitive.

$text = 'Be nice and respectful.';

if (ereg('nice', $text)){
  echo( '$text contains the string "nice".');
} else {
  echo( '$text does not contain the string "nice".');
}

ereg_replace - same as ereg plus it replaces every match of the regular expression with another string

eregi_replace - same except is not case sensitive.

$new_string = ereg_replace(regexp, replacewith, old_string);

special code	comment
A caret " ^ "	Marks start of text.
A dollar sign " $ "	Marks end of text.
Backslash " \ "	Prefix with a backslash to remove special meaning of a character.
Square brackets " [ ] "	Matches any string with any character within brackets.
Question mark " ? "	Trailing char is optional
Addition sign " + "	one or more of the previous char
Asterisk " * "	zero or more of the previous char
Period " . "	Matches any string of one or more char with no line breaks.
Parentheses " ( ) "	May be used to group string char together to apply ?, +, or * to them as a whole.

Examples:

Example	Result
[6789]	Matches 6, 7, 8, 9, or any text with those characters.
[6-9]	Same as [6789]
^[0-9]$	Matches any single number
^[a-z]$	Matches any single lower case letter
[0-9a-zA-Z]	Matches any string with a letter or number
^[a-zA-Z]+$	Matches any string of one ore more letters.
bana?na	Matches "banana" and "banna", but not "banaana".
bana+na	Matches "banana" and "banaana", but not "banna".
bana*na	Matches "banna", "banana", and "banaaana".
ba(na)+na	Matches "banana" and "banananana", but not "bana" or "banaana".

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
.=	String concatenation operator - adds a new string on the end of another string