php2

HTML forms contain at least the following elements:

A method: The method can be either POST or GET. Variables passed from a form to a PHP script are placed in the superglobal called $_POST or $_GET, depending on the form method.
An action
A submit button

In your HTML code, the first line of a form looks something like this:
"

Value 1:

Value 2:

Calculation:

add

subtract

multiply

divide

if (($_POST[val1] == "") || ($_POST[val2] == "") || ($_POST[calc] =="")) {
"