URL being doubled.. how to fix this?

[eluser]Unknown[/eluser]
hi! I'm a CI beginner, and I'm having this problem that whenever I go to another page, the url is doubled :
FROM this login view, the url is this : http://localhost/codeigniter/index.php/login

but when i click the login button it becomes like this : http://localhost/codeigniter/index.php/l...date_input

please help me