If we turn to your analogy with oil, then its value is determined not by the cost of production and transportation, but by demand as a source of energy resources.
In the same way, the market value of ether is determined not by the cost of its "production" and the direct cost of resources to execute smart contracts, but by the demand for the ...
You cannot directly iterate a mapping or enumerate the keys that exist because all keys in a hash table do definitely exist ... it's just that most of them have 0x0 values.
You can only solve the problem by creating a structure that uses a mapping for effective random access and an array for iteration. It's up to you to maintain the structure.
Have a look at ...
Mining pools have some threshold under which they don't pay mining rewards. So you need to contribute until you have reached that threshold and, after that, they should send you your rewards. The threshold is there to avoid extra transactions (each transaction costs).
The time it takes to reach the reward threshold depends mostly on your hashrate. So the ...
Some wallets will do this for you, but if you want to manually do it here's how:
Select a gas price before-hand. Let's say you want to use 100 gwei.
An ETH transaction costs 21000 gas, so you'll use 21*10^14 (21000 * 100 * 1E9) wei for the transaction. This is 0.0021 ETH.
Subtract 0.0021 ETH from your total amount and send that in the transaction.
If you ...
Currently Ethereum does not support using any other token as a gas currency except ETH.
Some custom wallets are working to support gas station network that would allow middleman to pay ETH on behalf of you. But in this case you end up paying the middleman the market rate of currency conversion.