another simple PHP page - php

Question

I'm trying to create a simple PHP page that will Display a number starting with 0. It will then ask for a number input, then add the inputted number to the beginning number. and keep adding the number that is input in the text box. Here's what I have so far... I can get the first variable initialized and get the input from a form box. I just can't seem to add them together and keep a running total. Thanks in advance.
<?php
$_POST['number1'];
echo "Current number is ".$_POST['number1'];
echo "<br>";
echo "Enter your next number.<br>";
echo "<form action='' method='POST'>";
echo "<input type='number' name='number2'>";
echo "<input type='submit' name='submit' value='Submit'>";
echo "<br>";
echo "Your entered number is ".$_POST['number2']."<br>";
$sumtotal = $_POST['number1'] + $_POST['$number2'];
echo "Your new total is ".$sumtotal;
$_POST['number1'] == $_POST['number2'];
?>

Answer 1

Using input type HIDDEN:
<?php
if(isset($_POST['submit'])){
$total=$_POST['number1']+$_POST['number2'];
echo "Your entered number is ".$_POST['number2']."<br>";
}
else {
$total=0;
}
echo "Current total number is ".$total;
echo "<br>";
echo "Enter your number.<br>";
echo "<form action='' method='POST'>";
echo "<input type='hidden' name='number1' value='$total'>";
echo "<input type='number' name='number2'>";
echo "<input type='submit' name='submit' value='Submit'>";
echo "</form><br>";
echo "Your new total is ".$total;
?>
Using SESSION:
<?php
session_start();
if(empty($_SESSION["total"])){
$_SESSION["total"]=0;
}
if(isset($_POST['submit'])){
$total=$_SESSION["total"];
$total=$total+$_POST['number2'];
$_SESSION["total"]=$total;
echo "Your entered number is ".$_POST['number2']."<br>";
}
echo "Current total number is ".$_SESSION['total'];
echo "<br>";
echo "Enter your number.<br>";
echo "<form action='' method='POST'>";
echo "<input type='number' name='number2'>";
echo "<input type='submit' name='submit' value='Submit'>";
echo "</form><br>";
echo "Your new total is ".$_SESSION['total'];
?>
Both works and have the same output, but with different approach from one another.

Answer 2

You could add another hidden input field that keeps the last number that was posted by you.
<input style="display: none" name="tmp_number" value="<?php echo $tmp_number; ?>">

Answer 3

Try (edited for all details and errors)
<?php
$input = $sum = 0;
if (isset($_POST)) {
$input = $_POST['number1'];
$prev_sum = $_POST['prev'];
$sum = $input + $prev_sum;
}
echo "Current number is ".$input;
echo "<br>";
echo "Enter your next number.<br>";
echo "<form action='' method='POST'>";
echo "<input type='number' name='number1'>";
echo "<input type='hidden' name='prev' value='$sum' >";
echo "<input type='submit' name='submit' value='Submit'>";
echo "<br>";
echo "Your entered number is ".$_POST['number1']."<br>";
echo "Your new total is ".$sum;
?>