Free Practice Questions for Blockchain CBDE Exam

Question 1

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.

Correct Answer: B. contract A.

Question 2

When a smart contract pays out money:

Ait's good to use a push over a pull method.

Bit'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.

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

Correct Answer: B. 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.

Question 3

Smart Contracts can be written in:

AJava, C++, Solidity and JavaScript, because the Ethereum Blockchain is completely language agnostic and cross compilers exist for every major language.

BSolidity, Viper, LLL and Serpent, because those are high level languages that are compiled down to bytecode.

CSolidity and JavaScript, because those are the official first implementations for Distributed applications and the Blockchain supports those languages fully.

Correct Answer: B. Solidity, Viper, LLL and Serpent, because those are high level languages that are compiled down to bytecode.

Question 4

Single line comments in Solidity are:

Aworking with either // or ///

Bworking with /* comment */ or /** @.. natspec style */

Cnot possible, all comments must be multi-line.

Correct Answer: A. working with either // or ///

Question 5

Proof of Work (PoW) vs. Proof of Stake.

APoW is computationally intensive which requires lots of energy. On the other hand, miners earn straightforward a reward for mining a block and incorporating transactions.

BPoW is better than PoS, because with PoS we increase the amount of energy spent on the network.

CPoS is mining with specialized new hardware that has to be purchased with a stack of Ether in the network. Hence the Name: Proof of Stake, which derives from Stack.

Correct Answer: A. PoW is computationally intensive which requires lots of energy. On the other hand, miners earn straightforward a reward for mining a block and incorporating transactions.

Question 6

Solidity files:

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

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

Ccan 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';'.

Correct Answer: 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';'.

Question 7

According to the official Style Guide:

Ayou should capitalize function names, events and contract names, to avoid confusion with JavaScript. You should use Tabs to indentation and a maximum of 80 characters per line.

Bcontract names should be capitalized, while functions should be mixedCase. You should use 4 spaces as indentation and a maximum of 79 (or 99) characters per line.

Ccontract should be mixedCase, as well as function names. Events should be capitalized. 2 spaces should be used as indentation and a maximum of 120 characters per line.

Correct Answer: B. contract names should be capitalized, while functions should be mixedCase. You should use 4 spaces as indentation and a maximum of 79 (or 99) characters per line.

Question 8

Block Timestamp:

Athe timestamp is based on the time zone of the miner, that is why it changes the difficulty continuously to reflect network latency.

Bthe timestamp can't be influenced by a miner and is generally considered safe to be used for randomness on the blockchain.

Cthe timestamp can be influenced by a miner to a certain degree but it's always independent from the time-zone.

Correct Answer: C. the timestamp can be influenced by a miner to a certain degree but it's always independent from the time-zone.

Question 9

What's the correct scientific notation?

A1 Ether = 10^18 wei, 10^9 Gwei, 10^3 Finney

B1 Ether = 10^19 wei, 10^13 Gwei, 10^3 Finney

C1 Ether = 10^16 wei, 10^13 Gwei, 10^3 Finney

D1 Ether = 10^18 wei, 10^6 Gwei, 10^6 Finney

Correct Answer: A. 1 Ether = 10^18 wei, 10^9 Gwei, 10^3 Finney

Question 10

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.

Correct Answer: C. returning Booleans to indicate an error during execution.