PHP

$$ in php

$x = "abc";  
$$x = 200;  
echo $x."<br/>";  
echo $$x."<br/>";  
echo $abc; 

// output:
abc
200
200

: in PHP

/*
This is an easy way to execute conditional html / 
javascript / css / other language code with 
php if else:

No need for curly braces {}
*/
<?php if (condition): ?>

// html / javascript / css / other language code to run if condition is true

<?php else: ?>

// html / javascript / css / other language code to run if condition is false

<?php endif ?>

? in php

/* 
in php, ? is the 'Ternary Operator'.

The expression (expr1) ? (expr2) : (expr3) evaluates 
to expr2 if expr1 evaluates to true, and expr3 if 
expr1 evaluates to false.

It is possible to leave out the middle part of the 
ternary operator. Expression expr1 ?: expr3 evaluates 
to the result of expr1 if expr1 evaluates to true, 
and expr3 otherwise. expr1 is only evaluated once in 
this case.
*/

<?php
// Example usage for: Ternary Operator
$action = (empty($_POST['action'])) ? 'default' : $_POST['action'];

// The above is identical to this if/else statement
if (empty($_POST['action'])) {
    $action = 'default';
} else {
    $action = $_POST['action'];
}
?>