/solidity-interview-questions

Solidity questions you can face during an interview

Solidity Interview Questions

This is a questions list you can be faced with in a Solidity focused interview.

Additional questions accepted via PR

Discalimer: This is not a complete package of questions guaranteeing you a job and is definitely incomplete. Depending on what position the candidate is applying for, the questions can be different, intuitive and also out of scope

Questions

Solidity

[Base 1]

  • What is mapping datatype?
  • default values in mappping(address => bool) ?
  • What does public visibilty mean?
    • internal vs private
  • view vs pure
  • Have you used openzeppelin
  • Fungible vs Non fungible
  • What are modifiers?
  • memory vs storage
  • What are the popular token standards?
    • Whats is the purpose for each?
  • What are some of the global variables?
  • What is a fallback function?
  • What solidity framework do you use?
    • How familiar are you with writing test suites

[Base 2]

  • What is variable default visibility uint a;
  • Have you used SafeMath?
    • Why?
  • What does _; in modifiers mean?
  • What is assembly in solidity;
  • What is keccak256?
  • What does abi.encodePacked do?
  • What contracts from Openzeppelin have you integrated excluding token standards?
  • What does indexed in events mean?
    • how many indexed params are permitted?
contract A {}
  • ^Can you send ether to the above contract?
  • transfer vs send vs call
  • What is re-entrancy?
  • What are oracles?
  • What are Meta txs?
  • What are upgradable contracts?
  • Have you interacted with any popular protocols programatically?
struct S {
  uint a;
}
mapping (uint => S) map;
function setValue() external {
  S memory s = map[1];
  s.a = 5;
}
function getValue() external view returns(uint256) {
  return map[1].a;
}
  • ^What would calling setValue() and then getValue() return?

Note: Skip moving to Base3 if the candidate's answers from Base2 are not convincing, Base3 should ideally be for senior/lead dev positions

[Base 3]

  • What does the memory address 0x40 point to?
  • Can you change the visibility of a variable in an upgradeable contract?
  • What is a stack too deep error and when can it occur?
    • Ways to resolve it?
  • How can you simulate transactions from someone else's address?
  • What is delegatecall
    • Who is msg.sender in a delegatecall?
  • Have you interacted with uniswap v3 oracle?
  • What is the create2 assembly opcode?
  • What are proxy contracts?
  • How would you generate a seemingly safe random number?