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<?phpif ($_SERVER['REQUEST_METHOD'] == "POST" && isset($_POST) && isset($_POST['action'])) {
 include_once 'Luhn.php';
 $luhn = new Luhn();
 if ($_POST['action'] == "calculate" && isset($_POST['gnumber'])) {
 $gnumber = $_POST['gnumber'];
 $gresult = $luhn->calculate($gnumber);
 } elseif($_POST['action'] == "validate" && isset($_POST['vnumber'])) {
 $vnumber = $_POST['vnumber'];
 if ($luhn->validate(substr($vnumber, 0, -1), substr($vnumber, -1, 1)) == true) {
 $vresult = "Number is valid";
 } else {
 $vresult = "Number is invalid";
 }
 }
 }
 ?><!DOCTYPE html>
 <html>
 <head>
 <title>Luhn's algorithm</title>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
 </head>
 <body>
 <div>
 <h1>Check digit calculation</h1>
 <form method="post">
 <input type="hidden" name="action" value="calculate" />
 <label for="gnumber">Number </label><input type="text" style="width: 300px;" id="gnumber" name="gnumber" value="<?php if (isset($gnumber)) echo $gnumber; ?>" /><br />
 Result <input type="text" style="width: 300px;" disabled="disabled" value="<?php if (isset($gresult)) echo $gresult; ?>" /><br />
 <input type="submit" value="Calculate" />
 </form>
 <h1>Number validation</h1>
 <form method="post">
 <p>Number must include check digit - last digit of number is check digit</p>
 <input type="hidden" name="action" value="validate" />
 <label for="vnumber">Number </label><input type="text" style="width: 300px;" id="vnumber" name="vnumber" value="<?php if (isset($vnumber)) echo $vnumber; ?>" /><br />
 Result <input type="text" style="width: 300px;" disabled="disabled" value="<?php if (isset($vresult)) echo $vresult; ?>" /><br />
 <input type="submit" value="Calculate" />
 </form>
 </div>
 </body>
 </html>
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