CBDE Sample Questions Answers

to check internal states that should never happen.

to check input arguments from users.

to check internal states that should never happen.

to check input arguments from users.

all gas is consumed.

all remaining gas is returned.

are interrupting execution on error, because they throw an exception.

continuing execution on error silently, which is the reason why they are so dangerous.

returning Booleans to indicate an error during execution.

.send() throws an exception, while the other functions are returning Booleans during execution to indicate an error.

the library you use must make use of the JSON-RPC Interface of an Ethereum Node.

must Implement the Ethereum Protocol to connect to other Ethereum Nodes.

must use Web3.js, which is closed source to communicate to other Ethereum Nodes.

it’s good to use a push over a pull method.

it’s good to use a push and a pull method to ensure that participants can get their money no matter the contract state. In addition to and pushing it should contain a withdraw method.

it's good to use only pull and no push method.

would be better, because it can reduce the amount of energy needed for mining.

would be worse, because it would increase the amount of energy needed for mining.

contract MyContractA is MyContractB { … }

contract MyContractA inherit (MyContractB) {…}

contract MyContractA extends MyContractB {…}

contract MyContractB derives MyContractA {…}

are stored on chain and are a great way to get a return value when a contract calls another contract.

are stored in something like a side-chain and cannot be accessed by contracts.

are used primarily for debugging exceptions in solidity.

to move all existing logic to the blockchain, so everything runs on the same system. This way it might be more complex, but easier to maintain.

to move only those parts to the blockchain that really need the blockchain. This way smart contracts can be easier to read, easier to test and are not so complex.

to move those parts to the blockchain that deal with Ether transfers. All other parts can remain in traditional database systems. This way only the value-transfer is on the blockchain.

is a must for every developer, because Web3.js changes so often.

is a convenient way because Web3.js is currently still in beta and truffle-contract can handle transactions with JavaScript-promises.

they are both completely different things. Truffle-Contract is a framework while Web3.js is a library.

for Java, JavaScript, and C++

for JavaScript using Web3.js

for Solidity and JavaScript

for any language, as long as it adheres to the open Testing-Interface from Truffle