| What is a gas in Ethereum? | The cost necessary to perform a transaction on the network |
| What is token in Etherium? | A token on Ethereum is basically just a smart contract that implements a standard functions that all other token contracts share. |
| What is a difference between ERC720 and ERC721 tokens? | ERC721 tokens are not interchangeable since each one is assumed to be unique, and are not divisible |
| What is pragma? | Pragmas are instructions to the compiler on how to treat the code |
| Is it possible to inherit from multiply contracts in Solidity? | Yes, separated by comma |
| What is the name of programming language using for Etherium? | Solidity. |
| What should we do if we have the modifier and the function of the same name? | We change a modifier, not function name, because the function name is standardized. |
| When receipt is fired and what does it mean? | receipt is fired when the transaction is included into a block on Ethereum, which means our zombie has been created and saved on contract |
| When error is fire and what does it do? | error is fired if there's an issue that prevented the transaction from being included in a block, such as the user not sending enough gas. It informs the user in our UI that the transaction didn't go through so they can try again. |
| What does the following code do?
.send({ from: userAccount })
.on("receipt", function(receipt) })
.on("error", function(error)){} | It send something from userAccount to blockchain and handle the result (receipt or error) |
| What is a Wei? | A wei is the smallest sub-unit of Ether — there are 10^18 wei in one ether. |
| For which purpose do we use the use the indexed keyword? | The indexed keyword is for filter events and only listen for changes related to the current user |
| How to query past events and filter their time range? | We can query past events using getPastEvents, and use the filters fromBlock and toBlock to give Solidity a time range for the event logs ("block" in this case referring to the Ethereum block number). |
| Is saving data expensive? | Yes. |
| How using events change the cost of saving data? | Using events for saving data is much cheaper in terms of gas. |
