CBDE Practice Exam Questions and Answers

A.  

totalSupply(), balanceOf(address), allowance(address,address), transfer(address,uint256), approve(address,uint256), transferFrom(address,address,uint256). Events: Transfer(address,address,uint256), Approval(address,address,uint256)

B.  

name(), symbol(), totalSupply(), balanceOf(address), ownerOf(uint26),approve(address,uint256), takeOwnership(uint256),transfer(address,uint256),Events: Transfer(address,address,uint256), Approval(address,address,uint256)

A.  

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

B.  

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.

A.  

to Wei, so it will send the equivalent of 10^18 Wei.

B.  

to Finney, so it will send the equivalent of 10^3 Finney.

C.  

to Szabo, so it will send the equivalent of 10^6 Szabo.

A.  

for which compiler version a smart contract was developed for. It helps to avoid breaking changes.

B.  

for which blockchain a smart contract was developed for. It helps to avoid confusion with beta-customers.

C.  

for which blockchain node a smart contract was developed for. It helps to avoid mixing up different versions of go-ethereum.

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.

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.

A.  

a Linked List with pointers to previous blocks hashes is used.

B.  

a Merkle Patricia Trie is used.

C.  

a Radix Trie is used because the Merkle Patricia Trie is too inefficient.

A.  

a function marked as pure can change the state, while a view function can only return static calls.

B.  

a function marked as view can never access state variables, while pure functions are here to return only one value.

C.  

a view function can access state variables, but not write to them. A Pure function cannot modify or read from state.

A.  

to check internal states that should never happen.

B.  

to check input arguments from users.

A.  

it always produces the same output given the same input.

B.  

it uses equally distributed data to produce the output given a long input.

C.  

it shouldn't be possible to re-generate the input given the output.

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.

A.  

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.

B.  

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.

C.  

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.

A.  

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

B.  

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.

C.  

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.

A.  

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

B.  

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

C.  

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

A.  

is the reference implementation of the Ethereum protocol and every other node implementation internally uses the closed-source from Geth.

B.  

is the library that is used for the blockchain node Go-Ethereum. It is also used by Parity is parts, because it's closed source.

C.  

is one of the many blockchain nodes that implement the Ethereum Protocol. It's open source and everyone can contribute.