<html>
<head>
    <title>Simple Calculator</title>
    <link href="//yorktown.cbe.wwu.edu/sandvig/mis314/assignments/style.css" rel="stylesheet" type="text/css">
</head>
<body>
    <div class="pageContainer centerText">
        <h2>Simple Calculator</h2>
        <hr />
        <form>
            <p>
                <label>Value 1: <input type="text" name="value1" autofocus></label><br><br>
                <label>Value 2: <input type="text" name="value2"></label><br><br>
                <input type="submit" value="Add">
            </p>
        </form>
        <?php
            //Retrieve name from querystring. Check that parameter
            //is in querystring or may get "Undefined index" error
            $value1 = $_GET['value1'];
            $value2 = $_GET['value2'];
            if (isset($value1) && isset($value2) && is_numeric($value1) && is_numeric($value2)) {
                echo "value1 = $value1<br>value2 = $value2<br>Sum is: ";
                echo ($value1 + $value2);
            } else {
                if (isset($value1) && isset($value2)) {
                    echo "Please enter valid numbers";
                }
            }
        ?>
    </div>
</body>
</html>
