How to subtract from a starting amount?-CodePudding

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 >
    <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 >
    <div id="matchn">
        <h3>Matchsticks left</h3>
        <h1><?=$mleft?></h1>
    </div>
</div>

CodePudding user response：

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 >
    <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 >
    <div id="matchn">
        <h3>Matchsticks left</h3>
        <h1><?=$mleft?></h1>
    </div>
</div>

CodePudding user response：

Now on every page refresh you declare $mleft = 36; and after second button press this variable is not e.g. 29, but 33. To fix it you can set $_SESSION variable, for example:

session_start(); // To set session variables tou must start it

if (!isset($_SESSION['mleft'])) { // Check if mleft exists, because setting up every 
    $_SESSION['mleft'] = 36;      // every page refresh will not 
}                                 // substract from variable


if (isset($_POST['pressed'])) {
    echo $_POST['pressed'];
    $_SESSION['mleft'] = $_SESSION['mleft'] -= $_POST['pressed'] ;  // Substract
    
}

CodePudding user response：

Just a friendly suggestion, you're probably a lot better off doing this in javascript like so...

let counterContainer = document.querySelector('h1');
let matchSticksLeft = parseInt(counterContainer.innerText);

function subtract(amount){
  counterContainer.innerText = matchSticksLeft -= amount;
}

<div >
    <button value=1 name="pressed" onclick="subtract(1)">1</button>
    <button value=2 name="pressed" onclick="subtract(2)">2</button>
    <button value=3 name="pressed" onclick="subtract(3)">3</button>
    <button value=4 name="pressed" onclick="subtract(4)">4</button>
</div>
<div >
    <div id="matchn">
        <h3>Matchsticks left</h3>
        <h1>36</h1>
    </div>
</div>