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2. Solidity 101.md

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Q1 Solidity language is

  • A) Statically typed

  • B) Object-oriented

  • C) Supports inheritance

  • D) Supports inline assembly

Click the reveal the answer A,B,C,D

Q2 Which of the following is/are correct?

  • A) A Solidity file with pragma solidity ^0.6.5; can be compiled with compiler version 0.6.6

  • B) A Solidity file with pragma solidity 0.6.5; can only be compiled with compiler version 0.6.5

  • C) A Solidity file with pragma solidity ^0.6.5; can be compiled with compiler version 0.7.0

  • D) A Solidity file with pragma solidity >0.6.5 <0.7.0; can be compiled with compiler version 0.7.0

Click the reveal the answer A,B

Q3 Which of the following is/are true?

  • A) Constant state variables can be initialized within a constructor

  • B) Immutable state variables are allocated a storage slot

  • C) Gas costs for constant and immutable variables is lower

  • D) Only value types can be immutable

Click the reveal the answer C,D

Q4 Solidity functions

  • A) Can be declared only inside contracts

  • B) Can have named return variables

  • C) Can have unnamed parameters

  • D) Can be recursive

Click the reveal the answer B,C,D

Q5 Function visibility

  • A) Goes from private-internal-external-public in decreasing restrictive order (i.e. private being the most restrictive)

  • B) Goes from internal-private-external-public in decreasing restrictive order (i.e. internal being the most restrictive)

  • C) May be omitted to default to internal in the latest 0.8.0+ compiler versions

  • D) None of the above

Click the reveal the answer A

Q6 Function foo() uses block.number. Which of the following is/are always true about foo()?

  • A) It should be marked as pure

  • B) It should be marked as view

  • C) It should be marked as payable

  • D) Cannot determine mutability based only on this information

Click the reveal the answer D

Q7 Which of the following is/are true about events?

  • A) Events are meant for off-chain applications

  • B) Events can be accessed only by the emitting contract

  • C) Indexing event parameters creates searchable topics

  • D) A maximum of three events can have indexed parameters

Click the reveal the answer A,C

Q8 A contract can receive Ether via

  • A) msg.value to payable functions

  • B) selfdestruct destination

  • C) coinbase transaction

  • D) receive() or fallback() functions

Click the reveal the answer A,B,C,D

Q9 receive() and fallback() functions

  • A) Can rely only on 2300 gas in the worst case

  • B) May receive Ether with payable mutability

  • C) Are mandatory for all contracts

  • D) Must have external visibility

Click the reveal the answer A,B,D

Q10 Which of the below are value types?

  • A) Address

  • B) Enum

  • C) Struct

  • D) Contract

Click the reveal the answer A,B,D

Q11 The default value of

  • A) Bool is false

  • B) Address is 0

  • C) Statically-sized array depends on the underlying type

  • D) Enum is its first member

Click the reveal the answer A,B,C,D

Q12 Address types

  • A) Can always receive Ether

  • B) Have members for balance, call, code

  • C) Can be converted to uint160 or contract types

  • D) Can be added and subtracted

Click the reveal the answer B,C

Q13 transfer and send primitives

  • A) Are used for Ether transfers

  • B) Trigger the receive() or fallback() functions of address

  • C) Always return a value to be checked

  • D) Provide only 2300 gas

Click the reveal the answer A,B,D

Q14 Which of the following is/are true for call/delegatecall/staticcall primitives?

  • A) They are used to call contracts

  • B) They only revert without returning success/failure

  • C) Delegatecall retains the msg.sender and msg.value of caller contract

  • D) Staticcall reverts if the called contract reads contract state of caller

Click the reveal the answer A,C

Q15 If we have an array then its data location can be

  • A) memory and its persistence/scope will be the function of declaration

  • B) storage and its persistence/scope will be the entire contract

  • C) calldata and it will only be readable

  • D) None of the above

Click the reveal the answer A,B,C

Q16 The impact of data location of reference types on assignments is

  • A) storage assigned to storage (local variable) makes a copy

  • B) memory assigned to memory makes a copy

  • C) memory assigned to storage creates a reference

  • D) None of the above

Click the reveal the answer D

Q17 Which of the following is/are valid control structure(s) in Solidity (excluding YUL)?

  • A) if

  • B) else

  • C) elif

  • D) switch

Click the reveal the answer A,B

Q18 The gas left in the current transaction can be obtained with

  • A) tx.gas()

  • B) gasleft()

  • C) msg.gas()

  • D) block.gaslimit()

Click the reveal the answer B

Q19 Which of the following is/are valid function specifier(s)?

  • A) internal

  • B) pure

  • C) payable

  • D) immutable

Click the reveal the answer A,B,C

Q20 Integer overflows/underflows in Solidity

  • A) Are never possible because of the language design

  • B) Are possible but prevented by compiler added checks (version dependent)

  • C) Are possible but prevented by correctly using certain safe math libraries

  • D) Are possible without any mitigation whatsoever

Click the reveal the answer B,C

Q21 Arrays in Solidity

  • A) Can be fixed size or dynamic

  • B) Are zero indexed

  • C) Have push, pop and length members

  • D) None of the above

Click the reveal the answer A,B,C

Q22 Structs in Solidity

  • A) Are user-defined type

  • B) Are reference types

  • C) Can contain or be contained in arrays and mappings

  • D) None of the above

Click the reveal the answer A,B,C

Q23 Which of the following is true about mapping types in mapping(_KeyType => _ValueType)?

  • A) _KeyType can be any value or reference type

  • B) _ValueType can be any value or reference type

  • C) Can only have storage (not memory) as data location

  • D) Can be iterated over natively (i.e. without implementing another data structure)

Click the reveal the answer B,C

Q24 if a = 1 then which of the following is/are true?

  • A) a += 1 makes the value of a = 2

  • B) b = ++a makes the value of b = 1

  • C) a -= 1 makes the value of a = 1

  • D) b = a-- makes the value of b = 1

Click the reveal the answer A,D

Q25 delete varName; has which of the following effects?

  • A) varName becomes 0 if varName is an integer

  • B) varName becomes true if varName is a boolean

  • C) No effect if varName is a mapping

  • D) Resets all struct members to their default values irrespective of their types

Click the reveal the answer A,C

Q26 Conversions in Solidity have the following behavior

  • A) Implicit conversions are never allowed

  • B) Explicit conversion of uint16 to uint8 removes higher-order bits

  • C) Explicit conversion of uint16 to uint32 adds lower-order padding

  • D) Explicit conversions are checked by compiler for safety

Click the reveal the answer B

Q27 If the previous block number was 1000 on Ethereum mainnet, which of the following is/are true?

  • A) block.number is 1001

  • B) blockhash(1) returns 0

  • C) block.chainID returns 1

  • D) block.timestamp returns the number of seconds since last block

Click the reveal the answer A,B,C

Q28 User from EOA A calls Contract C1 which makes an external call (CALL opcode) to Contract C2. Which of the following is/are true?

  • A) tx.origin in C2 returns A’s address

  • B) msg.sender in C2 returns A’s address

  • C) msg.sender in C1 returns A’s address

  • D) msg.value in C2 returns amount of Wei sent from A

Click the reveal the answer A,C

Q29 For error handling

  • A) require() is meant to be used for input validation

  • B) require() has a mandatory error message string

  • C) assert() is meant to be used to check invariants

  • D) revert() will abort and revert state changes

Click the reveal the answer A,C,D

Q30 The following is/are true about ecrecover primitive

  • A) Takes a message hash and ECDSA signature values as inputs

  • B) Recovers and returns the public key of the signature

  • C) Is susceptible to malleable signatures

  • D) None of the above

Click the reveal the answer A,C

Q31 When Contract A attempts to make a delegatecall to Contract B but a prior transaction to Contract B has executed a selfdestruct

  • A) The delegatecall reverts

  • B) The delegatecall returns a failure

  • C) The delegatecall returns a success

  • D) This scenario is not practically possible

Click the reveal the answer C

Q32 In Solidity, selfdestruct(address)

  • A) Destroys the contract whose address is given as argument

  • B) Destroys the contract executing the selfdestruct

  • C) Sends address’s balance to the calling contract

  • D) Sends executing contract’s balance to the address

Click the reveal the answer B,D