Editing PHP (section)

== Basic Syntax & Commands ==

PHP statements are always terminated with semicolon (;).

Single quotes are used to mark start and end of text (<nowiki>' '</nowiki>)

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

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

Example:

<code>$variable_name = "Semper Fidelis";</code>

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

Three ways to create comments. None of these are viewable to users via web browser.
* <code>//</code>
*<code>/* */</code>
*<code>#</code>

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

=== Concatenation ===

The concatenation operator, the period "." allows you to add strings of text.

Example:

<pre>$variable_name = "Hello" . " there" . " world!";

Assigns value of "Hello there world!" without quotes.
</pre>

Examples:

{| border="1" cellspacing="0" cellpadding="5" align="center"
! 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!'
|-
| \
| Escape character. Tells PHP to treat next character as text.
|}

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.


Some of PHP Built-In Functions

echo( "add_text" );

	passes a string

Variable interpolation = process of converting variable names to their values

Example:
$variable1 = 'PHP4';			// assigns variable1 the value "PHP4"
echo("$variable1 rocks!");		// output "PHP4 rocks!"
echo('$variable1 rocks!");		// output '$variable1 rocks!'



Arrays:
$variable = array('string1','string2',integer);


Integer indexes start from 0 and used to reference contents of array.


Examples:
echo($variable[0]);			// output "string1"
echo($variable[1]);			// output "string2"
echo($variable[2]);			// output "integer"
$variable[3] = 95;				// assigns 95 to 4th index (n-1)
$variable[0] = 'string0';		// assigns string0 to index 0.
$variable[] = 55;				// assigns 55 to end of array


Associative array:
Use a string as the index. Associate the value with index.
$phone['Joe'] = '555-1212';
$phone['Mike'] = '555-1313';

Example:
echo('Mikes phone number is ' . $phone['Mike']);

=== Predefined Variables ===

{| border="1" cellspacing="0" cellpadding="5" align="center"
! variable
! comment
|- 
| $_GET
|  is an associative array that PHP will automatically create so values
passed through a URL query string can be accessed.
|-
| $_SERVER
| is an array variable that contains information provided by the users
web browser
|}

=== Examples of using predefined variables ===

{| border="1" cellspacing="0" cellpadding="5" align="center"
! Example $_SERVER use
! comment
|-
| $_SERVER['PHP_SELF']
| Identifies the name of script being run. You can use to set browser to reference itself.
|-
| $_SERVER['HTTP_USER_AGENT']
| Identifies web browser and operating system accessing script
|-
| $_SERVER['REMOTE_ADDR']
| Identifies the IP address of the computer accessing script
|}

urlencode();
will convert special characters within input sting to special codes in order to appear
query string

isset();
outputs a true value if variable provided has been assigned a value

exit();
causes PHP to stop reading contents

die();
acts like echo(); immediately followed by exit();

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