CBDE Online Practice Questions and Answers

Solidity gets compiled:

A. to bytecode that can't be understood by humans.

B. to bytecodes which are essentially opcodes running instruction by instruction.

The nonce-field in a transaction is used:

A. to protect against replay attacks.

B. to have an additional checksum for transactions.

C. to sum up all ethers sent from that address.

Externally Owned Accounts:

A. can be destroyed using the selfdestruct keyword. This way all remaining ether will be sent to the receiver address, regardless if they have a fallback function or not.

B. are bound to a private key which is necessary to sign transactions outgoing from that account.

C. are logical opcodes running on the ethereum blockchain very similar to smart contracts.

To communicate with an Ethereum node via JavaScript:

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

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

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

Go-Ethereum vs. Ganache:

A. both are the same, just implemented in a different language.

B. with Go-Ethereum you get a real blockchain node where you can create your own local private network, connect to Test-Networks or the Main-Net, while with Ganache you get an in-memory blockchain simulation.

C. with Ganache you get a real blockchain node where you can connect to the Test-Networks Rinkeby and Ropsten.

Checking the balance of an address inside a loop of a smart contract constantly:

A. doesn't cost any gas.

B. cost gas every time we check the balance.

EVM assembly:

A. is much better than Solidity and a viable alternative.

B. can be split across multiple files, but every contract must be in a file with the same name as the contract itself.

C. is another language similar to LLL, more secure than Solidity.

Solidity files:

A. can't be split across multiple files, everything should be in one single file.

B. can be split across multiple files, but every contract must be in a file with the same name as the contract itself.

C. can be spread across multiple files. To import all contract from a file you can use "import 'myfile.sol'. To import Contract MyContract from myfile.sol you use "import {MyContract as SomeContract} from 'myfile.sol';".

Multi-Line Comments in Solidity are:

A. working with either // or ///

B. working with /* comment */ or /** @.. natspec style */

C. not possible, all comments must be single-line.

Address.send():

A. will cascade exceptions and address.transfer() will return a false on error.

B. will return false on error while address.transfer() will cascade transactions.

Why is it important to follow the same Interfaces?

A. Websites that try to interface with the Token would have to know the exact ABI. It is upfront clear how the interaction has to be with the standard Interfaces.

B. The Ethereum Foundation can easily validate the Tokens and approve any audits by following the standard interface.

When using assert to check invariants and it evaluates to false: A. all gas is consumed.

B. all remaining gas is returned.

It's easy to write clean-room unit-tests with truffle:

A. for Java, JavaScript, and C++

B. for JavaScript using Web3.js

C. for Solidity and JavaScript

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

With the truffle config file you can manage:

A. the amount of gas your contract deployment and transactions, against your contract, will need. This way you can essentially lower the gas costs over traditional web3.js dApps.

B. different Networks to deploy your contracts to. This way you can easily deploy to a local blockchain, the main-net or the Ropsten/Rinkeby Test-Net with only one parameter.

C. you can manage your secret API keys to the Ethereum Network. This way you can get access to several different Ethereum nodes at the same time without the need to switch your keyfiles.

Truffle has an integrated in-memory blockchain which makes unit-testing very easy:

A. True, but it's still good to use Ganache, or even a real private network for testing.

B. False, it's necessary to use Ganache or even a real private network for testing.