App to hardware

This may have been asked a million times, I am sorry if it has. I looked for it, but couldn't find it. I was wondering how I could have a c++ app on a computer communicate with a series of electronic switches. The App would receive an input from the hardware (like a completed circut) and then produce an output, like opening or closing a switch. I do not even know where to begin. Do they sell electronic switches that you can connect to a usb port, that come with an sdk (ideal world lol). Any suggestions would be great. Thanks guys.

You mean something like this?
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that may do it, I will need it to turn electromagnets on and off rapidly. This is why I may need my own application. Is it possible to use this chip with your own app? Does it come with an sdk (software development kit)?

I dunno if it has SDK, check the link. At $39. bucks most likely not. Here is another link.
**broken link removed**

Just google Digital IO, lots of companies make this stuff.

Take a look the link to the USB bitwacker in my signature. Also can be had assembled and test from sparkfun.com.