php variables (english)
Post on 12-Jul-2015
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Write by: Mahmood masih tehrani. .Www masihtehrani ir
.tehrani@dabacenter ir
PHP Variables
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.
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.
● ?>
PHP variable name is case-sensitive
● <?php
● $abc = 'Welcome';
● echo "Value of abc : $abc";
● echo "Value of ABC : $ABC";
● ?>
● <?php
● $height = 3.5;
● $width = 4;
● $area=$height*$width;
● echo "Area of the rectangle is : $area";
● ?>
PHP variables : Assigning by Reference
● <?php
● $foo='bob';
● $bar=&$foo;
● $bar="my $bar";
● echo $bar;
● echo '<br />';
● echo $foo;
● ?>
Output
● my bob
● my bob
PHP variable variables
● <?php
● $v='var1';
● echo $v; // prints var1
● $$v = 'var2';
● echo $$v; // prints var2
● echo $var1; // prints var2
● ?>
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".
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,
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 ";
● ?>
● 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
● The value of x is :
● The value of y is : 20
● The value of x is : 10
● The value of y is :
● 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.
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.
● <?php
● $x=2;
● $y=4;
● $z=5;
● $xyz=0;
● function multiple()
● {
● global $x, $y, $z, $xyz;
● $xyz=$x*$y*$z;
● }
● multiple();
● echo $xyz;
● ?>
● 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.
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.
● <?php
● function test_variable()
● {
● $x=1;
● echo $x;
● $x++;
● }
● test_variable();
● echo "<br>";
● test_variable();
● echo "<br>";
● test_variable();
● ?>
● 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.
● 1
● 1
● 1
● <?php
● function test_count()
● {
● static $x=1;
● echo $x;
● $x++;
● }
● test_count();
● echo "<br>";
● test_count();
● echo "<br>";
● test_count();
● ?>
● 1
● 2
● 3
The End
●Questian?
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