Newbie Question(s)

[nkcrpn]

Hello everyone. I'm not a newb to bitcoin, but to this particular forum, it would appear so. Since I must make a post to get out of here, I figured I'd get some questions answered while I'm at it.

The first, basic one: Why, when combining multiple addresses to make a BTC payment does change have to be sent back to the sender? And this only happens when multiple input addresses must be used, right?

Also, I've read the "original" eight page paper on Bitcoin, but what are some other sources for learning more about the ins and outs of bitcoin? (Besides here, ha ha ha...)

Lastly, a very niche question: I enjoy Android development and I'm about to release a paid app on the Play Store. Are there any Android app stores that support BTC payments? If not, what's the recommended way of setting it up myself? I've heard of Bitpay but I think they have some kind of minimum that I'm unlikely to reach. Would it be best to just manually do it for each person who wants to pay in BTC and send them the .apk once I've received payment?

Thanks so much!
Nick

[DannyHamilton]

The first, basic one: Why, when combining multiple addresses to make a BTC payment does change have to be sent back to the sender?

If you don't send the change somewhere then the miner (or mining pool) that confirms your transaction into a block gets to keep all of it as a transaction fee.  This is the design of bitcoin.  It prevents bitcoins from vanishing from existence while allowing outputs to be spent.

And this only happens when multiple input addresses must be used, right?

No.  This happens anytime the sum of the inputs is larger than the amount being sent.

Also, I've read the "original" eight page paper on Bitcoin,

If you missed the part about combining and splitting value and the use of "change", you might want to read it again.  I think you'll find that in section 9.

what are some other sources for learning more about the ins and outs of bitcoin? (Besides here, ha ha ha...)

Two of your best resources are here and reddit.  You can also learn quite a bit by looking at the source code of the Bitcoin-Qt (bitcoind) client.

Another good reference is the bitcoin wiki:
https://en.bitcoin.it/wiki/Main_Page

Beyond that, it would be a good idea to learn how to search using a search engine such as Google or Bing.

[infinitybo]

@Nkcrpn  You are not a newbie anyways it's sure BTC payments are emerging on some markets.