multiple forms saved in $_SESSION array

<?php
    session_start();
    echo 'Posted data: '; var_export($_POST);
    $step = isset($_POST['step'])? $_POST['step']:0; // received step, 0=no data
    if (!$step) { $_SESSION = array(); } //reset possibly received previous data, if any -optional
    $next_step = $step + 1;
    if ($step) { // if posted data available
        if (empty($_POST['i'.$step])) { //wrong received data detected
            echo 'Wrong data in this step!';
            $next_step = $step; // repeat this form
        } else {
            $_SESSION['i'.$step] = $_POST['i'.$step];
        }
    }
?><!DOCTYPE html>
<html>
<head>
  <title> http://stackoverflow.com/questions/11817574/build-a-link-format-in-php-like-step-1-etc </title>
</head>
<body>

<?php

function show_form() {
    global $next_step;
    if ($next_step==4) {
        echo '<b>All form fields succesfully obtained!</b>';
        var_export($_SESSION);
        return;
    }
    echo '<form action="" method="post">';
    if($next_step == 1) {
        // Display page 1
        echo 'Input 1 <input type="text" name="i1" value="">';
    }
    else if($next_step == 2) {
        // Display page 2
        echo 'Input 2 <input type="text" name="i2" value="">';
    }
    else if($next_step == 3) {
        // Display page 3
        echo 'Input 3 <input type="text" name="i3" value="">';
    }
    echo '<input type="hidden" name="step" value="'.$next_step.'">';
    echo '<input type="submit" name="send" value="Send">';
    echo '</form>';

    echo 'Current step='.$next_step.', data stored in session: '; var_export($_SESSION); //test
}

show_form();

?>

</body>
</html>