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

you can incorporate inline-assembly to get better controls.

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

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

Address.Call vs. Address.Delegatecall:

Address.call() is used for calling other contracts using the scope of the called contract in terms of storage variables. Address.delegatecall() is used for libraries, which uses the storage variables of the contract who called. Libraries are agreat way to re-use already existing code and delegatecall can make sure that no storage is used from the library, instead it looks like the code is directly copied into the calling contract.

Address.delegatecall() is used for calling other contracts using the scope of the called contract in terms of storage variables. Address.call() is used for libraries, which uses the storage variables of the contract who called. Libraries are agreat way to re-use already existing code and call() can make sure that no storage is used from the library, instead it looks like the code is directly copied into the calling contract.

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.

is a framework that helps developers with Testing, Deployment and Management of Smart Contracts and Distributed Applications.

is a library that helps developers to connect to Ethereum nodes, because it abstracts the JSONRPC interface.

is a framework for Java, similar to Web3.js for JavaScript. It's a great way to develop distributed Java enterprise applications.

Unit-Testing on a local chain is important, because it helps you:

to run tests quickly and especially for free, compared to continuous deployment on the MainNetwork. This way you save a lot of fees, time and costs.

to run tests in an environment where logging is activated. On the Main-Net you have no access to transaction logs and this is ultimately the information you need to debug your contracts.

to avoid regression bugs with contracts that are updated constantly on the main-net. Once you update a contract on the main-net, the address stays the same, but the code changes and this can have disastrous side-effects.

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

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

With the truffle config file you can manage:

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.

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.

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.

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 boxes are a great way:

to start with a pre-configured environment for most web-development needs.

to contribute to the box community which is the distributed file system for truffle.

to start with a pre-configured environment for most web-development needs.

to use tools that makes boxing of Dapps for different platforms very easy.

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

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

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

Using truffle-contract over Web3.js:

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

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.

Why is Unit-Testing so important?

It helps you to find bugs, regression bugs and sometimes also helps you to understand your code from different angles.

It is a great way to spend time on something that you get paid for. But ultimately it will just slow down the development process.

If you are starting a new ERC20 token:

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

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

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

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

To generate a random number:

it's good to use the RANDAO smart contract.

it's good to use the block timestamp, as this is always different.

it's good to use the block hash as this is clearly always very different.

it's good to use the RANDAO smart contract.

it's not possible to have a random number in a deterministic environment such as the Ethereum blockchain.

When you do external calls to other smart contracts:

you should follow the checks-effects-interactions pattern and avoid state changes after the call.

you should follow the effects-checks-interactions pattern and avoid state changes before the call.

you should follow the checks-effects-interactions pattern, which is only necessary when you do calls to contracts where a direct contract call is not possible.

When you are programming a game like poker of battleships where you need to hide opponents values is:

You can't hide anything on the blockchain, because the information is public, just the call is private which means only other smart contracts would be limited in accessing that information.

with private state variables. This way nobody else other than the smart contract itself can see the information

with external contracts holding those values. This way we can make sure that the information flow is following a clear logic and nobody else can access this information.

You can't hide anything on the blockchain, because the information is public, just the call is private which means only other smart contracts would be limited in accessing that information.

When considering smart contracts and the blockchain it's good:

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 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.

When a smart contract pays out money:

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 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.

To develop smart contracts:

it's good to start with a local in-memory blockchain with unit-tests. Then, in the next step, debug and test the smart contract on a test-net like Ropsten or Rinkeby with beta customers to iron out last issues before deploying it to the main- net.

it’s good to start with a local in-memory blockchain with unit tests but then deploy to the mainnet as rapidly as possible.

it's good to start with a local in-memory blockchain with unit-tests. Then, in the next step, debug and test the smart contract on a test-net like Ropsten or Rinkeby with beta customers to iron out last issues before deploying it to the main- net.

it's good to start with a test-net with beta-customers like on the Rinkeby or Ropsten testnet, before testing it locally on an in-memory blockchain simulation such as Ganache. Then deploy it to the main-net.

To avoid issues during Ethereum platform upgrades:

it's good to have the ability to pause a contract in order to manage the money at risk.

it's good to inform users about the updates via a newsletter.

it's good to have the ability to pause a contract in order to manage the money at risk.

Ethereum doesn't upgrade the platform. It's fixed and final.

Integrating the community into your testing:

is great, because they often find bugs which weren't considered before.

is not good, because you might give out secrets.

Blockchain CBDE Practice Test 3 - Free Online Exam Questions 81-102

Spam

Selling illegal goods, money scams etc.

Hate Speech

Serious attack on a group.

Harassment and bullying

Harassing an individual (including doxing)

Harmful activities

Threatening or glorifying violence or serious harm, including self-harm

Adult content (Consensual)

Nudity/Sexual content

Sexual exploitation and abuse (child safety)

Sexually explicit or suggestive imagery or writing involving minors

Sexual exploitation and abuse (adults and animals)

Sexually explicit or suggestive imagery or writing involving non-consenting adults or non-humans

Plagiarism

Reusing content without attribution (link and blockquotes)

Poorly written

Not in English or has very bad formatting, grammar, and spelling

Inappropriate credential

Author's credential is offensive, spam, or impersonation

Other

Ex. Illegal content, incomplete question...

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