Naming Conventions
- variables start with a
$sign, followed by the name of the variable. - variable names must start with a letter or the underscore character
_. - variable names cannot start with a number.
- variable names can only contain alpha-numeric characters and underscores (
A-z, 0-9, and _). - variable names cannot contain spaces.
Here are some examples:
<?php
$txt = "Hello world!";
$myNumber = 5;
$myFloat = 10.5;
echo $txt . "<br>";
echo $myNumber . "<br>";
echo $myFloat . "<br>";
Scope of Variables
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. There are three different variable scopes in PHP:
- local
- global
- static
Global Scope
Variables declared outside a function have global scope and can only be accessed outside a function. Below is an example:
<?php
$myGlobal = 5; // global scope
function myFunction() {
// using myGlobal inside this function will generate an error
echo "<p>Variable myGlobal inside function is: $myGlobal </p>";
echo "<br>";
}
myFunction();
echo "<p>Variable myGlobal outside function is: $myGlobal </p>";
echo "<br>";
Local Scope
Variables declared within a function have local scope and can only be accessed within that function: Below is an example:
<?php
function myFunction() {
$myLocal = 5; // local scope
echo "<p>Variable myLocal inside function is: $myLocal</p>";
echo "<br>";
}
myFunction();
// using myLocal outside the function will generate an error
echo "<p>Variable myLocal outside function is: $myLocal</p>";
echo "<br>";
The global keyword
The global keyword is used to access a global variable from within a function.
Below is an example on how the global keyword can be used.
<?php
$myFirstNum = 5;
$mySecondNum = 10;
function myFunction() {
global $myFirstNum, $mySecondNum;
$mySecondNum = $myFirstNum + $mySecondNum;
}
myFunction();
echo $mySecondNum; // outputs 15
The static keyword
After a function is executed, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. To do this, use the static keyword when first declaring the variable.
<?php
function myFunction() {
static $myLocal = 0;
echo $myLocal;
echo "<br>";
$myLocal++;
}
myFunction();
myFunction();
myFunction();
Each time the function(myFunction()) is called, that variable($myLocal) will still have the information it contained from the last time the function was called. Note that the variable($myLocal) is still local to the function.
Exercise
Create a variable named $myVar. Assign the value 1201 to the variable. Print the value of the variable.
<?php
$var = 123;
<?php
$myVar = 1201;
echo $myVar;
{
"test_output_contains":{
"expected":"1201",
"error_message":"Did you assign the correct value for <code>$myVar<\/code>?"
},
"test_variable_exists":{
"object":"$myVar",
"error_message":"Have you declared <code>$myVar<\/code>?"
},
"success_message":"Good job!",
"error_message":"Please read the instructions again."
}