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PHP Fundamentals
PHP Basic Syntax and Variables
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Week 2 – Basic Syntax and Variables
• How it all works
• PHP tags and statements
• Calling functions
• Concatenation
• Uniform Resource Locator - URL and the query string
• Form variables
• Variables and Literals
• Data types and Constants
• Variable scope
• All PHP language references can be found at www.php.net
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How PHP Works
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PHP Interpreter
PHP preprocessing
• PHP used to stand for “Pre-HyperText Processor” or Personal Home
Pages
• A request is made to the web server
• The web server locates the resource in this case a .php document
• The PHP interpreter is invoked, it reads the contents of the document,
executes all the code and returns the output
• The web server then returns the output back to the client ( browser )
• This can be text, html, a binary stream ( image )
• Quickly test online at
https://www.w3schools.com/php/phptryit.asp?filename=tryphp_intro
Be careful copying code from PowerPoint slides: the quotes
could be "smart quotes" instead of "straight quotes"
PHP Tags and Statements
PHP tags
• PHP code can be placed in a file with the extension .php
• PHP code is defined between an opening and closing tag.
<?php
?>
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PHP statement
• PHP statements are placed between an opening and closing PHP tag
and ALWAYS end with the semi-colon ; .
• All whitespace is ignored
<?php
echo '<h1>Hello world !</h1>';
?>
Placement of PHP
•PHP tags and their statements can be placed
repeatedly in a page, described as a “block of PHP or
PHP block”
<?php echo '<title>Welcome to My Website</title>'; ?>
<h1>Welcome to my page</h1>
<?php
//echo a list of products from our catalog
echo 'Here is the list';
?>
Basic PHP Example
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Common beginner's mistake: Opening
PHP page on local machine
▪This PHP script is
not processed by
the server
▪Chrome Browser
automatically
ignores the PHP
script in the output
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Running PHP
▪PHP scripts need to be processed by a webserver that
has a PHP engine installed
▪The output of that script is then sent to the client’s
browser
▪The PHP file will need to placed in the correct directory
on the web server and then accessed by the client’s
browser by using the correct server URL e.g.
http://localhost/mypage.php
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Accessing the PHP page
▪Viewing the source code from the browser
▪Do you see the original PHP script?
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Comments
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HTML Comments
▪HTML comments have the same syntax for both
multiline and single line comments
▪These are visible when the user views the page
source
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PHP Comments
•Comments in PHP are not interpreted and can be
single line or multi-line
<?php
// First let's do this single line comment
echo 'Time to get started !';
/*
* Then lets try this multi-line comment
*/
echo 'looks like we are doing this!';
?>
PHP Comments
▪Single line comments can also start with a hash #
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Calling PHP Functions
Built-in PHP Functions
•So far all we have done is output static text, we want to
output dynamic content, for example every time the page
loads, display the current day and time.
<?php
//output something like
//Hello, you loaded this page at 11 jan 2021 09:22 PM
echo 'Hello, you loaded this page at:' . date('d j Y
?>
h:i A');
PHP String Concatenation
• To join 2 strings of text or statement outputs together, join them using a
period
<?
//output Hello World as 2 strings, concatenated by a period
echo 'Hello' . ' World, today is ' . date('d');
?>
Looking up Built-in Functions in the PHP Manual
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PHP Manual
▪You can access the PHP manual online at php.net
▪If you are looking for a specific function, you can see
the details by going to: php.net/function
▪PHP date() function example:
php.net/date
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Uniform Resource Locator (URL)
URL
• A Uniform Resource Locator, also termed a web address, is a
reference to a web resource (i.e: an html page or image file) that
specifies its location on a computer network and a mechanism
for retrieving it.
http:// www.google.ca
http://
www.google.ca
/index.html
/index.html
- is the protocol
- is the hostname
- is the resource or file
URL Query String
• A URL can also transfer information through the web server.
http://www.yoursite.com/data.php?name=ryan
• The query string is defined after the special character ?
• ?name=ryan
• In the form of variable=value
• We divide each value pair by the special character &
name=ryan&course=php
Form Variables
• A URL can also transfer information through to the web server.
• PHP can access this data through a special superglobal variable called the $_REQUEST array
http://www.gofree.com/index.php?type=birds
<?php
//print the value of the variable "type" to the screen,
//it will print "birds"
echo $_REQUEST['type'];
?>
PHP Variables and Literals
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Literals
• A literal in PHP is the data itself. In this example it is a string.
When this code is run through the interpreter it will output the
exact string as it appears between the quotes
<?php
//the text below will output unchanged, it is literally a string
echo 'PHP is my favorite programming language, yay';
?>
PHP Variables
• While strings are the data, variables are symbols for the data. Variables
have a $ in front and can be assigned using the =
• A variable is created the first time you use it, you don’t have to declare
it. Must start with a letter or underscore. List of words NOT to use
• <?php
//Assign my string to my variable
$my_statement = 'PHP is my favorite programming language, yay';
//output the data stored in my variable
echo $my_statement;
?>
No Substitution in Literals
▪ For string literals, we use single quotes ' '
▪ If you want to substitute, or print, the data stored in the variable, ensure
that you use double quotes on a string
▪ Example:
$last_name = "Bedford";
//this will display correctly
print "My last name is $last_name";
//this will simply print $last_name, exactly as written
print 'My last name is $last_name';
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Data Types
Data Types
PHP supports the following basic data types:
• Integer - Used for whole numbers
• Float - Used for real numbers ( decimals )
• String - Used for string of characters
• Boolean - Used for true or false values
• Array - Used to store multiple data items
• Object - Used for storing instances of classes
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Data is Dynamically Typed
PHP will automagically change data types for the same variable
• <?php
//Assign my string to my variable
$my_statement = 'PHP is my favorite programming language, yay';
//change my variable to an integer
$my_statement = 12567;
//this will output the integer 12567 with no data type error
echo $my_statement;
?>
Printing Complex Data Types
▪Instead of print or echo, you can print out the value of
complex variables, such as arrays, using the print_r()
function
▪This is great for troubleshooting a script
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PHP Variable Names
▪PHP variables start with a dollar sign $
▪The variable MUST start with a letter or an underscore
▪ Example: $variable or $_variable
▪Afterwards, the variable name can contain letters, numbers, or
underscores
▪ Example: $_variable_name2
▪PHP variables are CaSe SenSitiVe
▪$_variableName is different than $_VariableName
▪PHP scripts will produce errors if the wrong variable name is
used when the script is executed
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Naming PHP Variables
▪PHP variables are recommended to use camel-hump
or camel-case naming conventions
▪Camel-hump example: $EmailAddress
▪Camel-case example: $email_address
▪Variable names should be named according to the
type of data they are storing
▪Good example: $phone_number
▪Bad example: $ph
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PHP Variables
▪You've seen that PHP variables do not to be declared
or initialized before they can be used
▪It is considered good practice to initialize variables
prior to using them. Do not risk printing a variable
without a value.
▪When declaring variables, comments should also be
used to describe the purpose of the variable’s use in
the script
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Working with Strings
▪PHP string variables can be problematic when it comes to the
use of quotation marks
▪Here are some examples of valid uses:
▪ "My name is $name"
▪ 'This course is awesome'
▪If you want to use quotation marks within the string, you will need
to escape the quotation mark
▪ "My name is \"Darryl\""
▪If you leave off a closing quote, the PHP interpreter gets
confused and may report the syntax error on a line below where
the actual error is
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PHP Array Variables
▪We will discuss Arrays in more detail later on in this
course
▪Arrays can contain more than one value
▪PHP uses two types of arrays:
▪Indexed array
▪Associative array
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Types of Arrays
Indexed Array
Key
Value
0
1
2
Ontario
British Columbia
Alberta
Associative Array
Key
Value
ON
BC
AB
Ontario
British Columbia
Alberta
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Constants
A constant is a name or an identifier for a fixed value. Constant are like variables,
except that once they are defined, they cannot be undefined or changed. Must
start with a letter or underscore
• <?php
//Define a constant
define('MY_STATEMENT', 'PHP is my favorite programming language, yay');
//use the constant
echo 'What is my fav language? ' . MY_STATEMENT;
?>
Variable Scope
Variable Scope
• The scope is the context in which a variable is defined. PHP only has local or global.
<?php
//Define variable in global scope
$my_global_var = 'something I may need everywhere';
//define a function that is local in scope
function myLocal()
{
//will output blank or be undefined because scope is local to this function
echo 'My variable contains: ' . $my_global_var;
}
myLocal(); //Calling the function
?>
PHP Variable Scope
▪And, PHP variables only exist on the PHP page that is
being executed. Once output is sent back to the
browser, the variable contents are gone
▪The exception are built-in superglobal variables that
begin with $_ and are all uppercase characters
Example: $_SERVER
▪More on those later
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Lab 02 Details
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Wrapping Up
•Any questions for me?
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