Variables and Assignment Operations

This section describes what is a variable, variable names prefixed with $, 'set' and 'unset' states of a variable, assigning data to variables, var_dump($var) to print variable information.

What is a variable? A variable is an identifier for a piece of data stored in memory during the program execution. In PHP, variables are used under these basic rules:

1. A variable name in PHP must be prefixed with a "$" sign. Perl has a similar rule for scale variables.

2. Variable names are case sensitive. So $address and $Address refer to two different variables.

3. Variables in PHP are typeless. Therefor there is no variable type declaration statements in PHP. Any variable can be used as the identifier for any data type.

4. A variable has 2 states: "set" and "unset". A variable is in the "set" state, if a piece of data has been assigned to it. A variable is in the "unset" state, if there is no data assigned to it.

5. Assignment operations (coded by the assignment operator, =) can be used to assign data to variables.

6. The unset($var) function can be used to remove the assigned data from the given variable.

7. Variables can used in any operations like data literals in PHP source code. If a variable with data assigned is used in an operation, the assigned data value will be used for the operation. If a variable with no data assigned is used in an operation, NULL will be used for the operation.

8. There are some special characters that you should not use them as part of a variable name, ' ', '$', '[', ']', '{', '}', ...

PHP has a nice built-in function, var_dump($var), that prints out detailed information about the specified variable.

To show you some of variable rules mentioned above, I wrote the following PHP script, VariableTest.php:

<?php # VariableTest.php
#- Copyright (c) 2015, HerongYang.com, All Rights Reserved.
# 
   print "\nVariable assignments:\n";
   
   $u; # Not assigning to any data
   print "\n   \$u: "; var_dump($u);

   $b = TRUE; # Assigning a boolean
   print "\n   \$b: "; var_dump($b);

   $i = 777; # Assigning an integer
   print "\n   \$i: "; var_dump($i);
   
   $f = 3.14; # Assigning a float
   print "\n   \$f: "; var_dump($f);

   $s = "Hello Herong"; # Assigning a string
   print "\n   \$s: "; var_dump($s);

   $a = array("Jan"=>31,"Feb"=>28); # Assigning an array
   print "\n   \$a: "; var_dump($a);

   $o = new DateTime(); # Assigning an object
   print "\n   \$o: "; var_dump($o);

   $r = opendir("."); # Assigning a resource
   print "\n   \$r: "; var_dump($r);

   $n = NULL; # Assigning NULL
   print "\n   \$n: "; var_dump($n);
?>

If you run this sample script, you should get:

Variable assignments:

   $u: NULL

   $b: bool(true)

   $i: int(777)

   $f: float(3.14)

   $s: string(12) "Hello Herong"

   $a: array(3) {
  ["Jan"]=>
  int(31)
  ["Feb"]=>
  int(28)
  ["Mar"]=>
  int(31)
}

   $o: object(DateTime)#1 (0) {
}

   $r: resource(4) of type (stream)

   $n: NULL

Last update: 2015.

Table of Contents

 About This Book

 Introduction and Installation of PHP 7.0

 PHP Script File Syntax

 PHP Data Types and Data Literals

Variables, References, and Constants

Variables and Assignment Operations

 References and Variables

 Variable Variable Name - Name Variables with Expressions

 Constant and define() Function

 Expressions, Operations and Type Conversions

 Conditional Statements - "if" and "switch"

 Loop Statements - "while", "for", and "do ... while"

 Function Declaration, Arguments, and Return Values

 Arrays - Ordered Maps

 Configuring and Sending out Emails

 Retrieving Information from HTTP Requests

 Creating and Managing Sessions in PHP Scripts

 Sending and Receiving Cookies in PHP Scripts

 Controlling HTTP Response Header Lines in PHP Scripts

 MySQL Server Connection and Access Functions

 Functions to Manage Directories, Files and Images

 SOAP Extension Function and Calling Web Services

 SOAP Server Functions and Examples

 Localization Overview of Web Applications

 Using Non-ASCII Characters in HTML Documents

 Using Non-ASCII Characters as PHP Script String Literals

 Receiving Non-ASCII Characters from Input Forms

 "mbstring" Extension and Non-ASCII Encoding Management

 Managing Non-ASCII Character Strings with MySQL Servers

 Introduction of Class and Object

 Integrating PHP with Apache Web Server

 Outdated Tutorials

 References

 PDF Printing Version