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?