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PHP Variables





A variable is a name given to a memory location which stores some data.

 

  • Each variable name must be started after using a dollar sign ($).
  • The name must be started with an alphabet or an underscore (_).
  • It may contain only alpha- numeric characters and underscores.
  • No space is allowed. Two words can be separated using underscore.
  • Variable names are case- sensitive.

Valid names- $var, $_var, $my_var, $MyVar, $variable345

Invalid names- $7var, $var%, $my var

 

    • There is no syntax for declaring a variable; therefore there is no need to declare a variable before using it.
    • No datatype is declared for a variable in php. Any variable can contain any type of value.
    • If a variable is used without assigning it a value, it will show an error.

<!DOCTYPE html>
<html>
<body>
<?php
$var1=35;$var2=45;
$sum=$var1+$var2; //Adding the two variables.
echo "The sum of ".$var1." and ".$var2." is ".$sum;
?>
</body>
</html>

Output

  • In above example, two variables var1 and var2 are created with values 35 and 45 respectively. A third variable sum is created and the addition of var1 and var2 is assigned to it. The variable sum is printed using echo statement. Read echo in PHP-Displaying Output.

 

  • The scope is the accessibility of the variables. It tells where a variable can be accessed from. The scope can be of two types-
    • Local- The accessibility of the variable is limited to a particular block or function.
    • Global- The variable can be accessed from anywhere in the document and from any function.

It can be understood by the following example-


<?php
$a=10;
function display()
{
echo "Inside the function<br>";
$a=20;
echo "a= ".$a."<br>";
$b=30;
echo "b= ".$b."<br>";
}
display();
echo "Outside the function<br>";
echo "a= ".$a."<br>";
echo "b= ".$b."<br>";
?>

Output

  • In above example, a variable a is created outside the functions so it can be used from anywhere in the code. When the function display() is called, the function creates a local variable a and prints it. Then it creates a new local variable b, assigns it a value and prints it.
  • Then a is directly printed from outside of the function and it prints the global value of this variable. But when we tried to print b, it displayed an error because b is not a global variable but it was created locally in the function display().
  • Note: You can also use the keyword global to access a global variable from a block.

Example

<?php$a=10;function display()

{

global $a;

}

Read functions in Functions.



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