how to get string before the second slash as a parameter??

You could use a routing rule, eg something like $route['(:any)/(:any)/(:any)'] = '$2/$1/$3';
See https://www.codeigniter.com/user_guide/g...uting.html

hi my friend

I tried to do what you say , but I couldn't to do that...

and I user this code in route.php :

$route['([a-zA-Z]+)'] = '?center=$1';

and

$route['([a-zA-Z]+)'] = 'index.php/?center=$1';

can you help me?