uninstall camera and reinstall on iPhone
You can't uninstall the Camera app as it is a built-in app. Instead, you will need to reinstall iOS by connecting the phone to iTunes over USB and clicking Restore in iTunes.

This also will allow you to back up the device and save your apps and content.

Lastly, Apple's warranty is worldwide and you can initiate service in the US online and via phone at http://support.apple.com and if you need a repair, they will give you options even if you are in India if it turns out to be hardware.