// calc.php

    <script type="text/javascript">

    /* <![CDATA[ */

    $(document).ready(function(){

    $('#calc').click(function(){

    var one = $('input[name="one"]').val();

    var two = $('input[name="two"]').val();

    var oper = $('select[name="oper"]').val();

    $.ajax({

    url: 'result.php',

    data: {one:one,two:two,oper:oper},

    success: function (data) {

    $('#result').html(data);

    $('#result').attr('disabled', false);

    },

    dataType: "html"

    });

    });

    });

    /* ]]> */

    </script>

     

    <input name="one" style="width: 50px;" type="text" />

    <select style="width: 50px;" name="oper">

    <option value="+">+</option>

    <option value="-">-</option>

    <option value="*">*</option>

    <option value="/">/</option>

    </select>

    <input name="two" style="width: 50px;" type="text" />

    <input type="submit" value="Считать" name="calc" id="calc" />

    <div id="result">

    <!-- AJAX -->

    </div>

     

    // result.php

    <?php

    $one = intval($_GET['one']);

    $two = intval($_GET['two']);

    $operator = $_GET['oper'];

     

    #file_put_contents('log.txt', $one . $operator . $two . PHP_EOL, FILE_APPEND | LOCK_EX);

     

    switch($operator){

    case '+':

    $result = $one + $two; break;

    case '-':

    $result = $one - $two; break;

    case '*':

    $result = $one * $two; break;

    case '/':

    if($two == 0)

    die('Делить на Ноль нельзя');

    else

    $result = $one / $two;

    break;

    default:

    return false;

    }

    echo '<b>Результат:' . $result . '</b>';

    ?>