The main way to store information in the middle of a PHP program is by using a variable.

• Here are the most important things to know about variables in PHP.
• All variables in PHP are denoted with a leading dollar sign ($).
• The value of a variable is the value of its most recent assignment.
• Variables are assigned with the = operator, with the variable on the left-hand side and
• the expression to be evaluated on the right.
• Variables can, but do not need, to be declared before assignment.
• Variables in PHP do not have intrinsic types - a variable does not know in advance
• whether it will be used to store a number or a string of characters.
• Variables used before they are assigned have default values.

• PHP does a good job of automatically converting types from one to another when
  necessary.
  PHP variables are Perl-lik
  PHP has a total of eight data types which we use to construct our variables:

• Integers: are whole numbers, without a decimal point, like 4195.

• Doubles: are floating-point numbers, like 3.14159 or 49.1.

• Booleans: have only two possible values either true or false.

• NULL: is a special type that only has one value: NULL.

• Strings: are sequences of characters, like 'PHP supports string operations.'

• Arrays: are named and indexed collections of other values.

• Objects: are instances of programmer-defined classes, which can package up both other kinds of values and functions that are specific to the class.

• Resources: are special variables that hold references to resources external to PHP
  (such as database connections).
  The first five are simple types, and the next two (arrays and objects) are compound - the
  compound types can package up other arbitrary values of arbitrary type, whereas simple
  types cannot.

Here's My PHP code

<?php
$x = 4;
function assignx () {$x = 0;
print "\$x inside function is $x.
";
}
assignx();
print "\$x outside of function is $x.
";
?>

This will produce the following result.

<?php
$x inside function is 0.
$x outside of a function is 4.
?>