Variables and Expressions in PHP

By the end of this post you will be able to:

  • Demonstrate how to use identifiers in PHP
  • Identify datatypes (float, integer, string etc)
  • Create variables in PHP
  • Identify global constants in PHP

What are PHP Identifiers/Variables?

An identifier is a general term or custom name applied to variables, functions and various other user defined objects.

The word identifier/variable is interchangeable in programming.  The best way to think of a variable is like a bucket that contains specific contents.
When defining variables you must note the following

  Variables must begin with a letter or underscore 

  _variableName

  You can camelCase variables
  
  Identifiers can_be_any_length

PHP has it’s own reserved variables

Identifiers must not have the same name as PHP’s own identifier names. A reference of PHP variable names can be located here: php.net/manual/en/reserved.variables.php

Create your own variables

Use this code as a starting point – change the variable name to display in browser.

<?php
  //Variables example 1
  $firstName = "Toby";
  $lastName = "Harris";
 
 /*You can echo out your variable without using speech marks.  
 Beware if you use single quotations it will not display the value  of  the variable but just the name of it.  
 Try it and see*/ 
 echo "$firstName $lastName";
?>

What’s happening here?

  • All PHP identifiers must be prefixed by the ‘$’ symbol.
  • We assign a value to the identifier or variable by using the ‘=‘ sign.
  • You can echo out the variable without the need to wrap it in quotation or speech marks
  • Or you can include the variable as part of a string

Data Types

What are data types?

  • Data types are containers
  • Each container is designed to hold different types of content

Most commonly used data types

String:  Alphanumeric characters 
Float:  Decimal 
Integer:  Whole numbers 
Boolean: True or false
Arrays:  Lists of items (Explored in lesson 6)
Null:  Nothing or zero

How are data types defined in PHP

PHP is referred to as a loosely type language:

  • Any identifier can hold any type of data
  • You do not need to declare the type data an identifier will hold

Let’s see some variables in action

Consider the code:

  • How are the variables defined?
  • How are they echoed out on to the screen?
$var1 = 'PHP'; // Assigns a value of 'PHP' to $var1
$var2 = 5; // Assigns a value of 5 to $var2
$var3 = $var2 + 1; // Assigns a value of 6 to $var3
$var2 = $var1; // Assigns a value of 'PHP' to $var2

echo "<ul>";
echo "<li>$var1 </li>"; // Outputs 'PHP'
echo "<li>$var2 </li>"; // Outputs 'PHP'
echo "<li>$var3 </li>"; // Outputs '6'
echo '<li>' . $var1 . ' is ace!</>'; // Outputs 'PHP is ace'
echo "<li>$var1 is ace! </li>"; // Outputs 'PHP is ace!'
echo '<li>$var1 is ace! </li>'; // Outputs '$var1 is ace!'
echo "</ul>"

A quick look at global constants and scope

Global constants

  • Global constants keep their state throughout the entire execution of a script
  • Example: Setting a VAT or shipping rate that applies throughout an application
  • Global constants by convention are defined in uppercase:
    define: ('VAT_RATE', 21.0 );

    or

    VATRATE

Some useful links

What have we explored in this post?

  • Demonstrate how to use identifiers in a PHP script
  • Identify data types in PHP (float, integer, string etc)
  • Create variables in PHP
  • Identify predefined variables in PHP (More in future lessons)
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