The document provides an overview of PHP variables, including their declaration, naming conventions, scope, and special types like variable variables and static variables. It explains that PHP variables start with '$', can include letters, numbers, and underscores, and are case-sensitive. The document also covers how to use global variables within functions and the concept of static variables to retain values between function calls.

1. PHP Variables
Write by: Mahmood masih tehrani
Www.masihtehrani.ir
tehrani@dabacenter.ir

2. Declaring PHP variables
● All variables in PHP start with a $ (dollar) sign followed by the name of
the variable.
●
● A valid variable name starts with a letter (A-Z, a-z) or underscore (_),
followed by any number of letters, numbers, or underscores.
●
● If a variable name is more than one word, it can be separated with
underscore (for example $employee_code instead of
$employeecode).
●
● '$' is a special variable that can not be assigned.

4. Valid and invalid PHP variables
● <?php
● $abc = 'Welcome'; //valid
● $Abc = 'W3resource.com'; //valid
● $9xyz = 'Hello world'; //invalid; starts with a number
● $_xyz = 'Hello world'; //valid; starts with an underscore
● $_9xyz = 'Hello world'; //valid
● $aäa = 'Hello world'; //valid; 'ä' is (Extended) ASCII 228.
● ?>

5. PHP variable name is case-sensitive
● <?php
● $abc = 'Welcome';
● echo "Value of abc : $abc";
● echo "Value of ABC : $ABC";
● ?>

6. ● <?php
● $height = 3.5;
● $width = 4;
● $area=$height*$width;
● echo "Area of the rectangle is : $area";
● ?>

7. PHP variables : Assigning by
Reference
● <?php
● $foo='bob';
● $bar=&$foo;
● $bar="my $bar";
● echo $bar;
● echo '<br />';
● echo $foo;
● ?>

8. Output
● my bob
● my bob

9. PHP variable variables
● <?php
● $v='var1';
● echo $v; // prints var1
● $$v = 'var2';
● echo $$v; // prints var2
● echo $var1; // prints var2
● ?>

10. PHP variable variables
● You know how to declare variables in PHP. But what if you
want the name your variable is a variable itself? In PHP,
you have Variable Variables, so you may assign a variable
to another variable.
● In the following example at line no. 2, we declared a
variable called $v which stores the value 'var1' and in line
no. 4, "var1" is used as the name of a variable by using
two dollar signs. i.e. $$v.
● Therefore there are two variables now. $v which stores the
value "var1" where as $$v which stores the value var2. At
this point $$v and $var1 are equal, both store the value
"var2".

11. PHP Variables Scope
● In PHP, variables can be declared anywhere in the script.
We declare the variables for a particular scope. There are
two types of scope,

12. Example
● <?php
● //global scope
● $x = 10;
● function var_scope()
● {
● //local scope
● $y=20;
● echo "The value of x is : $x "."<br />";
● echo "The value of y is : $y"."<br />";
● }
● var_scope();
● echo "The value of x is : $x"."<br />";
● echo "The value of y is : $y ";
● ?>

13. ● In the above script there are two variables
$x and $y and a function var_scope(). $x
is a global variable since it is declared
outside the function and $y is a local
variable as it is created inside the function
var_scope(). At the end of the script
var_scope() function is called, followed by
two echo statements. Lets see the output
of the script

14. ● The value of x is :
● The value of y is : 20
● The value of x is : 10
● The value of y is :

15. ● There are two echo statements inside var_scope() function. It prints
the value of $y as it is the locally declared and can not prints the value
of $x since it is created outside the function.
●
● The next statement of the script prints the value of $x since it is global
variable i.e. not created inside any function.
●
● The last echo statement can not prints the value of $y since it is local
variable and it is created inside the function var_scope() function.

16. The global keyword
● We have already learned variables
declared outside a function are global.
They can be accessed any where in the
program except within a function.
● To use these variables inside a function
the variables must be declared global in
that function. To do this we use the global
keyword before the variables.

17. ● <?php
● $x=2;
● $y=4;
● $z=5;
● $xyz=0;
● function multiple()
● {
● global $x, $y, $z, $xyz;
● $xyz=$x*$y*$z;
● }
● multiple();
● echo $xyz;
● ?>

18. ● In the above example $x, $y, $z, $xyz
have initialized with 2, 4, 5, 0. Inside
the multiple() function we declared $x,
$y, $z, $xyz as global. Therefore all
reference of each variable will refer to
global version. Now call multiple()
anywhere in the script and the
variable $xyz will print 40 as it is
already referred as global.

19. PHP static variables
● Normally when a function terminates, all
of its variables loose its values.
Sometimes we want to hold these
values for further job. Generally those
variables which holds the values are
called static variables inside a function.
To do this we must write the keyword
"static" in front of those variables.
Consider the following example without
static variable.

20. ● <?php
● function test_variable()
● {
● $x=1;
● echo $x;
● $x++;
● }
● test_variable();
● echo "<br>";
● test_variable();
● echo "<br>";
● test_variable();
● ?>

21. ● In the above script the function
test_count() is useless as the last
statement $x = $x +1 can not increase
the value of $x since every time it is
called $x sets to 1 and print 1.

22. ● 1
● 1
● 1

23. ● <?php
● function test_count()
● {
● static $x=1;
● echo $x;
● $x++;
● }
● test_count();
● echo "<br>";
● test_count();
● echo "<br>";
● test_count();
● ?>

24. ● 1
● 2
● 3

25. The End
●Questian?