Please read the documentation for both opendir and readdir before you continue. Please.

You need to use opendir first. If that succeeds, you can use readdir on the directory handle.

If you have trouble understanding what the documentation says, please feel free to ask questions... but it looks like you're randomly changing your code without understanding what you're doing (or understanding the advice people give you), and it's really frustrating to try to help you. Please help yourself and please, please help us help you.