is there any possibility if my code is not allowing google bots to read my website except robots.txt?

I have created a couple of website using CI 3.1.1 (PHP)
And none of them is being indexed on google even after all the tips and trick have been implicated which were suggested by google.

Is there anything in the code itself which could be the reason and not allowing google to index my pages.

Any help would be appreciated.

Thank You