I am using following code to generate menus

<?php 
$menu = array(); 
$menu['home'] = 'Home'; 
$menu['mypage'] = 'My Page'; 
//Add in the format of: $menu['page name'] = 'Page Title'; 
$title='Home'; //Default title 
function generateMenu()    { 
    global $menu,$default,$title; 
    echo '    <ul>'; 
    $p = isset($_GET['p']) ? $_GET['p'] : $default; 
    foreach ($menu as $link=>$item)    { 
        $class=''; 
        if ($link==$p)    { 
            $class=' class="selected"'; 
            $title=$item; 
        } 
        echo '<li><a href="?p='.$link.'"'.$class.'>'.$item.'</a></li>'; 
    } 
    echo '</ul>'; 
} 
?> 
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> 
<html> 
<head> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> 
<title>My PHP Template - <?php echo $title; ?></title> 
</head> 

<body> 
<?php 
generateMenu(); 
$default = 'home'; //Whatever default page you want to display if the file doesn't exist or you've just arrived to the home page. 
$page = isset($_GET['p']) ? $_GET['p'] : $default; //Checks if ?p is set, and puts the page in and if not, it goes to the default page. 
if (!file_exists('inc/'.$page.'.php'))    { //Checks if the file doesn't exist 
    $page = $default; //If it doesn't, it'll revert back to the default page 
    //NOTE: Alternatively, you can make up a 404 page, and replace $default with whatever the page name is. Make sure it's still in the inc/ directory. 
} 
include('inc/'.$page.'.php'); //And now it's on your page! 
?> 
</body> 
</html>

But I have 6 menus and first three menu have sub menus. Above code generates only menus. I want to add sub menu also.
Can anyone tell me HOW TO SOLVE THIS?

Well, there is so much information its hard to answer this one without knowing how you want your menus to display - especially with submenus, drops downs, etc you have many options, so its hard to give you an exact answer.

I am confident I can get you started though, you can tweak the code as needed. I changed a lot but I think I still covered all the functionality.

Feel free to ask question if you have any trouble.

<?php
// First, let's figure out your page
$page = $_GET['p']; // Get page name
if(empty($page)){$page = "home";} // Better to use empty instead of isset
//Check if page exists, otherwise set page to error 404 and set error 404 header:
if(!file_exists("inc/$page.php")){$page = "error404"; header("HTTP/1.0 404 Not Found");}


//Lets decide how the menu array should hold all the options
$menu = array();

$menu['home']['top'] = 'Home'; // ID of 0, top level navigation.
$menu['home']['sub page name'] = 'Sub Page'; // ID of 1, sub nav
$menu['home']['other sub page name'] = 'Other Sub Page'; // ID of 2, sub nav, etc

$menu['mypage']['top'] = 'My Page'; // ID of 0, top level navigation link.
$menu['mypage']['sub page name'] = 'Sub Page'; // ID of 1, sub nav
$menu['mypage']['other sub page name'] = 'Other Sub Page'; // ID of 2, sub nav, etc

function generateTitle(){
global $menu,$page;

foreach($menu as $k => $v){
  foreach ($v as $kk => $vv){
    if(($kk == "top" && $k == $page) || $kk == $page){
      return($vv);
    }
  }
}

}



//generate menu function
function generateMenu() {
global $page,$menu,$default,$title;

echo "<ul>";
foreach($menu as $k => $v){
foreach ($v as $kk => $vv){
if($kk == "top"){
echo "<li><a href=\"?p=$k\"";
if($k == $page){echo " class=\"selected\"";}
echo ">$vv</a></li>";
echo "<ul>";
}else{
echo "<li><a href=\"?p=$kk\"";
if($kk == $page){echo " class=\"selected\"";}
echo ">$vv</a></li>";
}

}
echo "</ul>";
}

echo "</ul>";
}

//Doctype needs to be put on page before ANY white space, so it has to be directly after the closing php ">" symbol, I like to echo it out in the PHP to make sure though:

echo "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01//EN\" \"http://www.w3.org/TR/html4/strict.dtd\">";

?>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>My PHP Template - <?php echo generateTitle(); ?></title>
</head>

<body>
<?php
generateMenu();
include('inc/'.$page.'.php'); //And now it's on your page!
?>
</body>
</html>

It's great work DUDE!!!

Well, there is so much information its hard to answer this one without knowing how you want your menus to display - especially with submenus, drops downs, etc you have many options, so its hard to give you an exact answer.

I am confident I can get you started though, you can tweak the code as needed. I changed a lot but I think I still covered all the functionality.

Feel free to ask question if you have any trouble.

<?php
// First, let's figure out your page
$page = $_GET['p']; // Get page name
if(empty($page)){$page = "home";} // Better to use empty instead of isset
//Check if page exists, otherwise set page to error 404 and set error 404 header:
if(!file_exists("inc/$page.php")){$page = "error404"; header("HTTP/1.0 404 Not Found");}


//Lets decide how the menu array should hold all the options
$menu = array();

$menu['home']['top'] = 'Home'; // ID of 0, top level navigation.
$menu['home']['sub page name'] = 'Sub Page'; // ID of 1, sub nav
$menu['home']['other sub page name'] = 'Other Sub Page'; // ID of 2, sub nav, etc

$menu['mypage']['top'] = 'My Page'; // ID of 0, top level navigation link.
$menu['mypage']['sub page name'] = 'Sub Page'; // ID of 1, sub nav
$menu['mypage']['other sub page name'] = 'Other Sub Page'; // ID of 2, sub nav, etc

function generateTitle(){
global $menu,$page;

foreach($menu as $k => $v){
  foreach ($v as $kk => $vv){
    if(($kk == "top" && $k == $page) || $kk == $page){
      return($vv);
    }
  }
}

}



//generate menu function
function generateMenu() {
global $page,$menu,$default,$title;

echo "<ul>";
foreach($menu as $k => $v){
foreach ($v as $kk => $vv){
if($kk == "top"){
echo "<li><a href=\"?p=$k\"";
if($k == $page){echo " class=\"selected\"";}
echo ">$vv</a></li>";
echo "<ul>";
}else{
echo "<li><a href=\"?p=$kk\"";
if($kk == $page){echo " class=\"selected\"";}
echo ">$vv</a></li>";
}

}
echo "</ul>";
}

echo "</ul>";
}

//Doctype needs to be put on page before ANY white space, so it has to be directly after the closing php ">" symbol, I like to echo it out in the PHP to make sure though:

echo "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01//EN\" \"http://www.w3.org/TR/html4/strict.dtd\">";

?>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>My PHP Template - <?php echo generateTitle(); ?></title>
</head>

<body>
<?php
generateMenu();
include('inc/'.$page.'.php'); //And now it's on your page!
?>
</body>
</html>

My css for dynamic menus

<style media="all" type="text/css"> 
body { background: #0D1114; }
ul,li{ list-style:none;}
ul { border: 1px solid #eee; border-bottom: 0; }
li { background: #fff; border-bottom: 1px solid #eee; }
li li { background: #eee; }
a { padding: 0 10px; font: bold 13px/30px 'Arial', 'sans-serif'; color: #036; text-decoration: none; }
</style>

Please Help me to create Accordion

Well, there is so much information its hard to answer this one without knowing how you want your menus to display - especially with submenus, drops downs, etc you have many options, so its hard to give you an exact answer.

I am confident I can get you started though, you can tweak the code as needed. I changed a lot but I think I still covered all the functionality.

Feel free to ask question if you have any trouble.

<?php
// First, let's figure out your page
$page = $_GET['p']; // Get page name
if(empty($page)){$page = "home";} // Better to use empty instead of isset
//Check if page exists, otherwise set page to error 404 and set error 404 header:
if(!file_exists("inc/$page.php")){$page = "error404"; header("HTTP/1.0 404 Not Found");}


//Lets decide how the menu array should hold all the options
$menu = array();

$menu['home']['top'] = 'Home'; // ID of 0, top level navigation.
$menu['home']['sub page name'] = 'Sub Page'; // ID of 1, sub nav
$menu['home']['other sub page name'] = 'Other Sub Page'; // ID of 2, sub nav, etc

$menu['mypage']['top'] = 'My Page'; // ID of 0, top level navigation link.
$menu['mypage']['sub page name'] = 'Sub Page'; // ID of 1, sub nav
$menu['mypage']['other sub page name'] = 'Other Sub Page'; // ID of 2, sub nav, etc

function generateTitle(){
global $menu,$page;

foreach($menu as $k => $v){
  foreach ($v as $kk => $vv){
    if(($kk == "top" && $k == $page) || $kk == $page){
      return($vv);
    }
  }
}

}



//generate menu function
function generateMenu() {
global $page,$menu,$default,$title;

echo "<ul>";
foreach($menu as $k => $v){
foreach ($v as $kk => $vv){
if($kk == "top"){
echo "<li><a href=\"?p=$k\"";
if($k == $page){echo " class=\"selected\"";}
echo ">$vv</a></li>";
echo "<ul>";
}else{
echo "<li><a href=\"?p=$kk\"";
if($kk == $page){echo " class=\"selected\"";}
echo ">$vv</a></li>";
}

}
echo "</ul>";
}

echo "</ul>";
}

//Doctype needs to be put on page before ANY white space, so it has to be directly after the closing php ">" symbol, I like to echo it out in the PHP to make sure though:

echo "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.01//EN\" \"http://www.w3.org/TR/html4/strict.dtd\">";

?>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>My PHP Template - <?php echo generateTitle(); ?></title>
</head>

<body>
<?php
generateMenu();
include('inc/'.$page.'.php'); //And now it's on your page!
?>
</body>
</html>