Blockchain CBDE Exam Practice Test Instant Access

Question 1

If you are starting a new ERC20 token:

Ait would be best to start from scratch, just looking at the required interface.

Bit is beneficial to copy and paste the already existing code from the Ethereum wiki and modify this until you like it.

Cbest is to start with an audited implementation, for example from OpenZeppelin, in order to reuse already existing code.

Answer : C

Question 2

If you need more fine-grained functionality than solidity offers out of the box:

Ayou can incorporate inline-assembly to get better controls.

Byou have to import pre-compiled assembly files which are then hard-copied into the bytecode of the compiled solidity file.

Cyou can use Viper, the experimental assembly like language specifically to offer more flexibility.

Answer : A

Question 3

Using selfdestruct(beneficiary) with the beneficiary being a contract without a payable fallback function:

Awill throw an exception, because the fallback function is non-payable and thus cannot receive ether.

Bit's impossible to secure a contract against receiving ether, because selfdestruct will always send ether to the address in the argument. This is a design decision of the Ethereum platform.

Cselfdestruct doesn't send anything to a contract, it just re-assigns the owner of the contract to a new person. Sending ether must be done outside of selfdestruct.

Answer : B

Question 4

All low-level functions on the address, so address.send(), address.call.valueQQ, address.callcode and address.delegatecall:

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

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

Creturning Booleans to indicate an error during execution.

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

Answer : C

Question 5

The difference between address.send() and address.transfer() is:

A.send returns a Boolean and .transfer throws an exception on error. Both just forward the gasstipend of 2300 gas and are considered safe against re-entrancy.

B.send throws an exception and .transfer returns a Boolean on error. Both just forward the gasstipend of 2300 gas and considered safe against re-entrancy

C.send returns a Boolean and .transfer throws an exception on error. .send is considered dangerous, because it sends all gas along, while .transfer only sends the gas stipend of 2300 gas along

D.send and .transfer are both considered low-level functions which are dangerous, because they send all gas along. It's better to use address.call.value()() to control the gas-amount.

Answer : A

Question 6

Loops in Solidity:

Aare a great way to circumvent gas requirements, because a loop will only consume gas once.

Bare dangerous when used with data structures that grow, such as arrays or mapping, because it is hard to estimate the gas requirements.

Cshould be avoided where possible, because of unknown side-effects on the gas requirements.

Answer : B

Question 7

If a User calls contract A and that calls Contract B, then msg.sender in Contract B will contain the address of:

Athe User.

Bcontract A.

Answer : B

Blockchain CBDE BTA Certified Blockchain Developer - Ethereum Exam Practice Test