Modern wallets do this for you behind the scenes they have reserved change addresses to handle this, same as calculating the fee from inputs and outputs. You would need to put this into account in case you would want to create a raw tx by yourself. 
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Ah ok ok 
Couldnāt wrap my head around it, but now I understand. Thanks!
Thank you for the information.
When you want to do a tx, does the wallet generate all the UTXOs assigned to your wallet or just the UTXOs that sum to the required amount for the transaction?
A wallet will cherry pick as many UTXOs as it requires to fund the tx. Using all UTXOs as inputs to a tx would be a waste because the tx would be larger and you would have to pay a larger fee in that case.
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I guess this is a pretty old thread, but I was intrigued by the notion of initiating crypto transactions without the internet and started researching this. Turns out thereās now a project called Allohash that purports to do exactly that, i.e., allow users to initiate crypto transactions via SMS or voice authorization.
https://bitrss.com/news/196513/allohash-the-offline-cryptocurrency-exchanger
(Note: this is a link to a paid press release, not an independent article. I am not affiliated or trying to promote their product, just thought this is a cool innovation that speaks to what I just learned in Bitcoin 101 
)
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There is also Blockstream satellite but can technically only receive blocks to sync the node with it. But you can use a combination of these technologies to send the tx and be synced with the blockchain.
Hello,
I have 2 questions:
a) miners are now rewarded for each mined block in BTC, after all blocks are mined they will be rewarded by transaction fees, due to this will the fees drasticaly increase to make it interesting enough for miners to keep the network live?
b) out of 21 000 000 BTC we could say there is going to be maybe 4 000 000 (if not more) impermanently lost, hypoteticaly, could there be a consensus made that these coins that are confirmed to be lost, are returned into the circulation ? somewhere i was reading that if 51% of network comes to consensus they could make this happen and make other changes in the ledger.
Looking forward for your opinions.
Karel
additional question:
i have just found 12 word passphrase but i do not know what wallet/account it belongs to, so how do i go around and find what is in there ?
No one knows what will happen after that this will happen somewhere in the year 2140 when the block reward will finally be dropped to 0.
That would mean stealing funds from some random addresses that are considered āstolenā. I donāt think it can be done and if it can it would require a hard fork that I would refuse to follow and I doubt a lot of people would. It would just end up in another BCH/SV version of a Bitcoin fork.
You can import the seed in any HD (hierarchical deterministic) wallet to find out.
Thank you for all answers!
I hope some smart minds are going to work on this and think how to prevent the whole Bitcoin operation from crushing in 119 years from now 
Thought so it would be considered stealing and that would just invalidate the whole idea.
Im goin to research more on this HD wallet, thanks for the tip 
Hi! When transactions are extracted from the mempool, how is it ensured that a transaction is not picked by 2 separate miners and added to 2 different blocks? I assume this could happen due to latency if miner A picks transaction X and miner B also picks transaction X before his mempool gets the chance to be updated. When miner Bās mempool eventually updates, does he stop mining, replace the removed transaction and restarts mining? That would sound like a waste of time and resources.
If a miner would mine a block with an invalid tx the network would simply reject it. Canāt do much about that if he already mined a block with an invalid tx its to bad for him.
In case of a stale block a tx could exist in both blocks at the time but eventually one block would be dropped in that case.
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I am having a difficult time finding the website with the blockchain simulator. I could find the video Ivan is on the site but I canāt find the name of the site.
Lets take the following scenario:
- A miner chooses to take all the lowest fee transactions to the block
- The miner makes a mistake that is perfectly valid like a small change to one of the transactions
- Miner manages to get the block to the blockchain and other miners choose to continue this version of the truth
How can anyone find this mistake in time? What if it takes 100 blocks to find it?
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Thank you, you are a scholar and a gentleman.
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If its a valid transaction then it would be accepted as valid, there would be no mistake to find. Using smaller txs would not change that in any way. If the tx is invalid though the nodes would not accept the block once they receive it.
If youāre talking about the malleability issue it was solved with the Segwit update that moved the witness data out of the tx structure which makes impossible to change given its a segwit type tx. If for example someone would to change the witness then the withess hash would be different than its stored in the tx which would basically make the output impossible to spend.
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Thank you. For now Iām assuming that any miner can 100% verify the validity of a block as soon as they see it. Iām sure it will come up later in more detail.
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Yes. ThatĀ“s why the phrase: āNot your key - not your money.ā The one who has the private key has control over the funds on this adress.
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