9x9gridWithMarkedX.php

<style>
    td {
        border: 1px solid black;
        margin: 2px;
        padding: 2px;
    }
    .marked {
        background-color: red;
    }
</style>

<table>
    <?php
    $rows = 9;
    $columns = 9;

    for ($i=1; $i<=$rows; $i++)
    {
        ?>
        <tr>
            <?php
            for ($c=1; $c<=$columns; $c++)
            {
                $marked = '';
                if (($i == 1 || $i == 9) && ($c == 1 || $c == 9))
                    $marked = 'marked';
                elseif (($i == 2 || $i == 8) && ($c == 2 || $c == 8))
                    $marked = 'marked';
                elseif (($i == 3 || $i == 7) && ($c == 3 || $c == 7))
                    $marked = 'marked';
                elseif (($i == 4 || $i == 6) && ($c == 4 || $c == 6))
                    $marked = 'marked';
                elseif ($i == 5 && $c == 5)
                    $marked = 'marked';
                ?>
                <td class="<?php echo $marked; ?>"></td>
                <?php
            }
            ?>
        </tr>
        <?php
    }
    ?>
</table>