CBDE Online Practice Questions and Answers

Smart Contracts can be written in:

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

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

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

Having a bug-bounty program early on:

A. can help to engage the community in testing your smart contracts and therefore help to find bugs early.

B. might be a burden as it is an administrative overhead mainly.

C. is completely useless. Who wants to test beta-ware software? It's better to start with the bug-bounty program after the contract is released on the main-net.

Block Difficulty:

A. is determined by the Ethereum Committee every fortnight to reflect the average amount of transaction and it cannot be influenced by the network itself.

B. increases when the time between mined blocks is below 10 seconds, while it decreases when the time is above 20 seconds.

C. increases when the time between mined blocks is below 20 seconds, while it decreases when the time is above 60 seconds.

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.

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';".

The following are value types in Solidity.

A. Integer, Boolean, Struct, Mapping and Enum.

B. Integer, Boolean, Enum and Addresses.

C. Integer, Boolean, Structs and Fixed Point Numbers.

View and Pure Functions: A. can only be accessed during calls.

B. can be accessed during transactions and calls.

Assert is used:

A. to check internal states that should never happen.

B. to check input arguments from users.

.Require is used:

A. to check internal states that should never happen.

B. to check input arguments from users.

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.