Fatal Error: Unsupported Operand Types

How to fix Fatal error: Uncaught TypeError: Unsupported operand types: string + string [PHP] [HTML]

to fix the current implementation

you need to add the switch statements inside the try block,
so when the validation exception fire it will escape running it
and about showing the error beside the input you can set the exception message in a variable and print it beside the input " ,

your implementation after those edits will looks like :

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Calculator</title>
</head>

<?php

$number1 = "";
$number2 = "";
$result = "";
$calculate = "";
$number1Error = '';

if (isset($_GET['calculate'])) {
    $number1 = $_GET['number1'];
    $number2 = $_GET['number2'];
    $calculate = $_GET['calculate'];
    $errors = [];
    
    function isValidNumber1($number1)
    {
        if (!is_numeric($number1)) {
            throw new Exception("Number 1 is not a number!");
        }
    }
    
    
    try {
        isValidNumber1($number1);
        $result = $number1 + $number2;
        
        switch ($calculate) {
        case "Add":
        var_dump($number1);
            $result = $number1 + $number2;
            break;
        case "Substract":
            $result = $number1 - $number2;
            break;
        case "Multiply":
            $result = $number1 * $number2;
            break;
        case "Divide":
            $result = $number1 / $number2;
            break;
        case "Modulo":
            $result = $number1 % $number2;
            break;
    }
    
    } catch (Exception $e) {
        $number1Error = $e->getMessage() . PHP_EOL;
        
    }

    
}

?>

<body>
    <h1>Calculator</h1>

    <form action="" method="get" id="calculator">

        <label for="number1">Number 1: </label>
        <input type="text" name="number1" value="<?php echo $number1; ?>"> <?php echo $number1Error; ?><br><br>
        <label for=" number2">Number 2:</label>
        <input type="text" name="number2" value="<?php echo $number2; ?>"><br><br>

        <?php
        echo "<p>Operation:  $calculate</p>";
        echo "<p>Result: $result</p>";
        ?>

        <div>
            <input type="submit" name="calculate" value="Add">
            <input type="submit" name="calculate" value="Substract">
            <input type="submit" name="calculate" value="Multiply">
            <input type="submit" name="calculate" value="Divide">
            <input type="submit" name="calculate" value="Modulo">
        </div>
    </form>

</body>

</html>

Fatal error: Uncaught TypeError: Unsupported operand types: string * string

$row['price'] and $_POST['quantity' . $iterate] return strings which can not be multiplied. So you have to convert both to int values:

$subt = (int)$row['price']* (int)$_POST['quantity' . $iterate]

PHP Fatal error: Uncaught Error: Unsupported operand types when adding values to array

That is because $supergroupnew is not defined inside the function and the actual error would read:

Notice: Undefined variable: supergroupnew

You need to make the following small change:

array_walk_recursive($supergroup, function($item, $key) use($id, &$supergroupnew) {
// removed & from id
// added &$supergroupnew to use statement, you can access/modify this external variable

Having said that, using += on arrays will create a union instead of appending. Quote:

The + operator returns the right-hand array appended to the left-hand
array; for keys that exist in both arrays, the elements from the
left-hand array will be used, and the matching elements from the
right-hand array will be ignored.

You should use [] instead unless there is something I don't understand.

Fatal Error: Unsupported Operand Types

How to fix Fatal error: Uncaught TypeError: Unsupported operand types: string + string [PHP] [HTML]

Fatal error: Uncaught TypeError: Unsupported operand types: string * string

PHP Fatal error: Uncaught Error: Unsupported operand types when adding values to array

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