Which iPhone SDK to use for compatibility

i'm writing my first iPhone app with aim to upload it to the AppStore and don't understand one thing:

Most popular games on the AppStore have compatibility with iPhone OS 3.0 or later. I have currently installed iPhone SDK 4.0开发者_开发问答 i believe.

I want my app to have the same compatibility starting from 3.0, do i have to install and use in development an earlier SDK, like 3.0 to achieve that goal or i can somehow use the latest SDK?

Thanks for any help!

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You should always build against the most current SDK, that is 4.1 at the moment. You can set your minimum requirement differently though, i.e. 3.0.

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To be able to upload your application to appstore you must build it using SDK 4.0 at least.

Then in build target settings you can specify minimum OS version your application can be run on - check "iPhone OS Deployment Target" setting.

Remember that if you use some APIs that are available not on all OS versions you support you should do run-time checks for them to avoid application crashes.