Sessions and Forms in PHP

Let's say we have two PHP files. Let's place a form in the file test1.php that asks the user for two numbers:

<form method="GET">
	<input name="num1">
	<input name="num2">
	<input type="submit">
</form>

In the same file, let's place the form processing code. In this code, we will write the input data to the session:

<?php
	session_start();
	
	if (!empty($_GET)) {
		$_SESSION['num1'] = $_GET['num1'];
		$_SESSION['num2'] = $_GET['num2'];
	}
?>

An important nuance: in the file, the form processing code must be placed before the form itself. Why: because in this code we are working with the session, and therefore there should be no output to the screen before this.

Now let's find the sum of the numbers stored in the session in the file test2.php:

<?php
	if (!empty($_SESSION)) {
		echo $_SESSION['num1'] + $_SESSION['num2'];
	}
?>

In what sequence should this all work? First, the user goes to the page test1.php, fills out the form, and clicks the button. After that, they land again on test1.php, but now with the submitted form data. At the same time, they enter the condition in which we write the form data to the session.

Then the user must manually go to the page test2.php - and there they will see the sum of the entered numbers.

You might ask: why complicate things like this? After all, the form could have been immediately sent to the page test2.php. The thing is, that in this case, the convenience lies in the fact that the form itself and the code for its processing are located on the same page. This, of course, is not always convenient, but sometimes it is necessary.

On one page, using a form, ask the user for their last name, first name, and age. Write this data to the session. When accessing another page, display this data on the screen.