How to Redirect all HTTP requests to HTTPS? This Query is unique

I recently have moved to HTTPS version from HTTP. But since then, I am into trouble and problem is not solved. So, my query is, How to redirect user to HTTPS version of site regardless whatever he types. For ex., Let me explain:-

example.com --->>> `https:// www.example.com/

www.example.com --->>> https:// www.example.com/

https:// example.com --->>> https:// www.example.com/

Moreover, If in future I make my mind to move site to https:// example.com instead of https:// www.example.com, then what will be the code for this? Let me give example for this too.

example.com --->>> https:// example.com/

www.example.com --->>> https:// example.com/

https:// www.example.com --->>> https:// example.com/

I have seen that if a user types https:// example.com and I want it to redirect to https:// www.example.com/ then browser give warning about its security before redirecting. Hence, asks for users confirmation. This is bad thing and can destroy site owner image. This should not happen. :D

Please suggest .htaccess code for both types separately. For info, using Apache Web Server. :D