Untitled

<?php
session_start();
class Example{
    /**
     * Inicialize
     */
    public function __construct()
    {
        if(empty($_SESSION['value']))
        {
            $_SESSION['value'] = 0;
        }

    }

    public function setValue()
    {
        $_SESSION['value']++;
    }

    public function getValue($value='')
    {
        return $_SESSION['value'];
    }
}


$example = new Example;

if(isset($_POST['submit']))
{
    $example->setValue();
}

?>

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <link href="http://getbootstrap.com/dist/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
    <div class="container">
        <div class="col-md-4">
            <form action="" method="POST" role="form">
                <legend>Valor: <?php echo $example->getValue(); ?></legend>

                <button name="submit" value="submit" type="submit" class="btn btn-primary">Depositar</button>
            </form>
        </div>
    </div>
</body>
</html>