BLOCKCHAIN - BTA Certified Blockchain Developer - Ethereum

1.

Loops in Solidity:

are a great way to circumvent gas requirements, because a loop will only consume gas once. are dangerous when used with data structures that grow, such as arrays or mapping, because it is hard to estimate the gas requirements. should be avoided where possible, because of unknown side-effects on the gas requirements. B

2.

Events:

are stored on chain and are a great way to get a return value when a contract calls another contract. are stored in something like a side-chain and cannot be accessed by contracts. are used primarily for debugging exceptions in solidity. B

3.

According to the official Style Guide:

you 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. contract names should be capitalized, while functions should be mixedCase. You should use 4 spaces as indentation and a maximum of 79 (or 99) charactersper line. contract should be mixedCase, as well as function names. Events should be capitalized. 2 spaces should be used as indentation and a maximum of 120characters per line. B

4.

Variables of the type address store:

a 20 bytes value a 32 bytes value a string a 20 characters long hex number A

5.

Address.send():

will cascade exceptions and address.transfer() will return a false on error. will return false on error while address.transfer() will cascade transactions. B

6.

Address.call.value():

sends the gas stipend of 2300 gas and returns a false on error. sends all the gas along and cascades exceptions. sends all the gas along and returns a false on error. sends the gas stipend of 2300 gas and cascades exceptions. C

7.

Address.send() and address.transfer() are considered:

safe against reentrancy because of the small gas stipend of 2300 gas. dangerous because they send all gas along, it's better to use address.call.value()(). B

8.

When defining a new datatype:

its best to use a contract with public storage variables, so it can be used like a class. it's best to use a struct, which is cheaper than deploying a new contract. it's not possible to generate new datatypes in Solidity. B

9.

What is the difference between ERC20 and ERC721 Tokens in simple terms?

The tokens of a certain ERC20 symbol are all the same, the tokens of an ERC721 symbol are all different. So, ERC20 tokens are fungible, while ERC721 tokens are non-fungible. The tokens of a certain ERC20 symbol are all different, the tokens of an ERC721 symbol are all the same. So, ERC20 tokens are non-fungible while ERC721tokens are fungible. A

10.

In order to implement an ERC20 token contract, you'd need at least to implement the following functions and events in order to fulfill the interface requirements:

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) 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

BLOCKCHAIN - BTA Certified Blockchain Developer - Ethereum

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