How to subtract from a starting amount?

February 3, 2022

I am a beginner at coding and I am printing a number (36 here) and I have 4 buttons. Pressing each button should subtract from the amount remaining. So when I press the ‘3’ button, the amount remaining is 33 but after this when I press the button ‘4’, the value displayed should be 29, but what I get is 32 instead.

How do I make it so the value of variable mleft is not reset to 36 each time I press a button?

<div class="bt_grp">
    <form method="post">
        <button value=1 name="pressed">1</button>
        <button value=2 name="pressed">2</button>
        <button value=3 name="pressed">3</button>
        <button value=4 name="pressed">4</button>
    </form>
</div>
<?php 
$mleft = 36;
if (isset($_POST['pressed'])) {
    echo $_POST['pressed'];
    $mleft = $mleft -= $_POST['pressed'] ;
    
}
?>

<div class="flex-container">
    <div id="matchn">
        <h3>Matchsticks left</h3>
        <h1><?=$mleft?></h1>
    </div>
</div>

>Solution :

Each time you post the form, you set $mleft to 36 before you subtract from it.

If you want the value to persist between calls, use a session variable and subtract from that.

<?php
session_start();
?>

<div class="bt_grp">
    <form method="post">
        <button value=1 name="pressed">1</button>
        <button value=2 name="pressed">2</button>
        <button value=3 name="pressed">3</button>
        <button value=4 name="pressed">4</button>
    </form>
</div>
<?php 
$mleft = $_SESSION['mleft'] ?? 36;
if (isset($_POST['pressed'])) {
    echo $_POST['pressed'];
    $mleft -= $_POST['pressed'] ;
}
$_SESSION['mleft'] = $mleft;
?>

<div class="flex-container">
    <div id="matchn">
        <h3>Matchsticks left</h3>
        <h1><?=$mleft?></h1>
    </div>
</div>