PHP Variables

As with algebra, PHP variables can be used to hold values (x=5) or expressions (z=x+y).

A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume).

Rules for PHP variables:

• A variable starts with the $ sign, followed by the name of the variable
• A variable name must start with a letter or the underscore character
• A variable name cannot start with a number
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Variable names are case sensitive ($y and $Y are two different variables)

Creating (Declaring) PHP Variables

PHP has no command for declaring a variable.
A variable is created the moment you first assign a value to it:

Example

<?php
   $txt="Hello world!";
   $x=5;
   $y=10.5;
?> 

After the execution of the statements above, the variable txt will hold the value Hello world!, the variable x will hold the value 5, and the variable y will hold the value 10.5.

Note: When you assign a text value to a variable, put quotes around the value.

PHP is a Loosely Typed Language

 In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically converts the variable to the correct data type, depending on its value.

In other languages such as C, C++, and Java, the programmer must declare the name and type of the variable before using it.

PHP Variables Scope

In PHP, variables can be declared anywhere in the script.
The scope of a variable is the part of the script where the variable can be referenced/used.
PHP has three different variable scopes:

• local
• global
• static

Local and Global Scope

A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function.

A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function.

The following example tests variables with local and global scope:

<?php
  $x=5; // global scope

 function myTest() {
  $y=10; // local scope
  echo "<p>Test variables inside the function:</p>";
  echo "Variable x is: $x";
  echo "<br>";
  echo "Variable y is: $y";
}

myTest();

echo "<p>Test variables outside the function:</p>";
echo "Variable x is: $x";
echo "<br>";
echo "Variable y is: $y";
?>

 In the example above there are two variables $x and $y and a function myTest(). $x is a global variable since it is declared outside the function and $y is a local variable since it is created inside the function.

When we output the values of the two variables inside the myTest() function, it prints the value of $y as it is the locally declared, but cannot print the value of $x since it is created outside the function.

Then, when we output the values of the two variables outside the myTest() function, it prints the value of $x, but cannot print the value of $y since it is a local variable and it is created inside the myTest() function.