How to define dynamic variable in php?

If you need to define variable dynamically in php then this can be done easily.
Say, your variable name will be ‘dynamic_variable_name’

Generally we define php variable normally as $normal_variable; but in this case we would like to create dynamically.
Then we have to write something like following way:

$normal_variable = 'dynamic_variable_name';
${$normal_variable} = 'New dynamic variable created';
echo $dynamic_variable_name;
// prints New dynamic variable created.

To explain it better I am giving an instance which will be very helpful to develop PHP sites and reduce some hard work.

I have a form as given below:

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
First Name : <input type="text" name="first_name"><br />
Last Name : <input type="text" name="last_name"><br />
<input type="submit" name="submit" value="Submit" >
</form>

While you submit the form, capture all variables and values:

if(!empty($_POST)){
	foreach($_POST as $variable => $key){
		${$variable} = trim($key);
	}
        echo $first_name . '  ' . $last_name;
}