17 – Difference Between $ and $$ in PHP
This tutorial will focus on the difference between $ and $$ PHP To start with, let’s review first what is PHP Variables.
PHP Variable plays a vital role in PHP programming. It allows you to store information in computer memory.
To declare a PHP variable, it starts with a dollar sign($) like as shown in the syntax below
PHP Variable Syntax:
<?php $variableName = "value"; ?>
$$ Meaning in PHP (Double Dollar Variable)
The PHP $$ (double dollar) variable is a reference variable that stores the value which is accessible by using $ Symbol(Single Dollar) variable value
They call it sometimes as a variable variable name. Wherein the variable name can be set and used dynamically.
Below examples illustrate the use of $ and $$ in PHP
<?php $myvar = "PHP"; echo $myvar; ?>
[su_box title=”Output Will Be:” radius=”7″ ]PHP[/su_box]
Here’s the $$ in PHP Example
<?php $myvar = "PHP"; $myvar = "Programming!"; echo $myvar. '<br/> '; echo $myvar. '<br/> '; echo $PHP. '<br/> '; ?>
[su_box title=”Output Will Be:” radius=”7″ ]
PHP
Programming!
Programming!
[/su_box]
Another Complex Example of $$ in PHP
<?php
$myvar = "PHP";
${$myvar}="Programming";
${${$myvar}}="Is Fun!";
echo $myvar . "<br/>";
echo $PHP . "<br/>";
echo $Programming . "<br/>";
echo ${${$myvar}}. "<br/>";
?>[su_box title=”Output Will Be:” radius=”7″ ]
PHP
Programming
Is Fun!
Is Fun!
[/su_box]
We will discuss what we have in the above code using PHP Double dollar and Dollar Variables
- First, we declare and initialize the variable.
- Then, reference the variable
- Next, we use the double reference variable
- Finally, we display the value of the variable.
- Lastly, we display a double reference.
Note:
If you have any questions about the $$ in PHP example, please feel to contact us or simply leave a comment below.
Frequently Asked Questions
How does this PHP project work?
Built with vanilla PHP (no framework) and MySQL backend. Standard structure: form HTML, PHP script handlers, MySQL via PDO or mysqli, sessions for auth, Bootstrap for responsive layout. Ready to extend for BSIT capstone scope.
What PHP and MySQL versions does this project require?
Most projects in this batch run on PHP 7.4 to PHP 8.2 with MySQL 5.7+ or MariaDB 10+. A few older projects need PHP 5.6 (deprecated, use XAMPP 7.x). To run: install XAMPP / WAMP / Laragon, extract project to htdocs, import the included .sql file via phpMyAdmin, edit the connection file (usually config.php or db_connect.php) with your DB credentials, browse to the project URL in your browser.
How do I set up the database for this PHP project?
Open phpMyAdmin (http://localhost/phpmyadmin/ on XAMPP), create a new empty database with the name specified in the project’s config.php. Click the Import tab, choose the included .sql file, click Go. Then edit config.php (or includes/connection.php) with: ‘localhost’, your MySQL username (usually ‘root’), your MySQL password (usually blank for XAMPP), and the database name.
Can I use this PHP project for a BSIT capstone or thesis?
Yes, but extend it. A bare CRUD app is too narrow for full capstone scope. Add: user roles via session checks, reports/dashboards (Chart.js + AJAX), PDF exports (TCPDF library), email notifications (PHPMailer), real domain extension (analytics, audit log, multi-branch support). Pair with Chapter 1-5 documentation matching your panel’s rubric.
Why am I getting ‘connection error’ or ‘undefined function mysqli_connect’?
Three common PHP issues: (1) Connection error: Apache + MySQL services not running in XAMPP control panel, OR database name in config.php does not match what you created in phpMyAdmin. (2) ‘undefined function mysqli_connect’: MySQL extension not enabled, in php.ini uncomment extension=mysqli (then restart Apache). (3) ‘No such file or directory’: MySQL socket path wrong, use 127.0.0.1 instead of localhost in the connection string.
Where can I find more PHP projects with source code?
Browse the PHP Projects hub for the full library (300+ vanilla PHP systems). For modern PHP MVC alternatives see Laravel Projects (74 systems) or CodeIgniter Projects (32 systems). For BSIT-focused capstone idea lists see 150 Best Capstone Project Ideas.