How can PHP be used to display error messages when a form is submitted with a default value in a select box?

When a form is submitted with a default value selected in a select box, PHP can be used to check if the default value is submitted and display an error message accordingly. This can be done by checking the value of the select box in the form submission handling code and displaying an error message if the default value is detected. 

<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $selectValue = $_POST['select_box'];
    
    if ($selectValue == 'default') {
        echo "Please select a valid option from the dropdown menu.";
    } else {
        // Process the form submission
    }
}
?>

<form method="post" action="<?php echo $_SERVER['PHP_SELF']; ?>">
    <select name="select_box">
        <option value="default">Select an option</option>
        <option value="option1">Option 1</option>
        <option value="option2">Option 2</option>
        <option value="option3">Option 3</option>
    </select>
    <input type="submit" value="Submit">
</form>

Keywords

PHP form submission select box error messages default value

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