Prepare for your Solidity developer interview with this comprehensive guide featuring 30 essential questions and answers. Covering basic, intermediate, and advanced topics, these questions target freshers, candidates with 1-3 years, and 3-6 years of experience in smart contract development.
Basic Solidity Interview Questions (1-10)
1. What is Solidity and what is it primarily used for?
Solidity is a statically-typed, high-level object-oriented programming language designed for developing smart contracts that run on the Ethereum Virtual Machine (EVM).[5]
2. What are the main components of a Solidity smart contract?
The main components include pragma statement, state variables, constructor, functions, modifiers, events, and inheritance support for code reuse.[3][5]
3. Explain the difference between storage and memory variables in Solidity.
Storage variables are persistent and stored on the blockchain, making them expensive in gas costs, while memory variables are temporary and only exist during function execution.[1]
4. What are the visibility modifiers in Solidity functions?
The visibility modifiers are public (accessible externally and internally), private (only internally), internal (within contract and inherited contracts), and external (only externally).[2]
5. What is a pragma statement in Solidity?
The pragma statement specifies the required Solidity compiler version for the contract, ensuring compatibility, such as 6. What is a constructor in Solidity? A constructor is a special function executed once during contract deployment to initialize state variables.[3][5] 7. Explain events in Solidity. Events are custom data structures that emit transaction logs, allowing external applications to monitor contract activity and state changes.[3][5] 8. What are modifiers in Solidity? Modifiers are reusable code snippets added to functions to modify their behavior, commonly used for access control or preconditions like 9. How do you define state variables in Solidity? State variables store persistent data on the blockchain and are declared at contract level, such as 10. What does the Solidity compiler produce? The Solidity compiler (solc) translates code into EVM bytecode and ABI for deployment and interaction.[1][3] 11. What is the difference between view and pure functions? View functions read state but don't modify it, while pure functions neither read nor modify state and can't access storage.[6] 12. Explain mappings in Solidity with an example. Mappings store key-value pairs like where balances[msg.sender] retrieves a user's balance.[4] 13. How does inheritance work in Solidity? Contracts can inherit from base contracts using 14. What is msg.value in Solidity? msg.value represents the amount of Ether sent with a function call, checked in payable functions.[6] 15. Explain require, assert, and revert in Solidity. require validates inputs and refunds gas, assert checks invariants and consumes all gas on failure, revert undoes state changes.[1] 16. How do you create a simple voting contract structure? Define mappings for votes, an array of candidates, and functions to vote and retrieve results with owner restrictions.[1] 17. What are libraries in Solidity? Libraries are reusable code with internal functions, deployed once and linked via DELEGATECALL for gas efficiency.[2] 18. Explain the difference between external and public functions. External functions can only be called from outside the contract and use calldata efficiently, while public can be called both internally and externally.[2] 19. How do you handle errors in Solidity 0.8.0+? Use custom errors for gas-efficient reverts, declared as 20. What is a fallback function in Solidity? Fallback is a special function triggered when no matching function is found or Ether is sent directly, marked as 21. What changed with arithmetic in Solidity 0.8.0? Solidity 0.8.0 introduced built-in overflow checks for arithmetic operations, reverting on overflow/underflow instead of wrapping around.[2] 22. Explain CREATE vs CREATE2 opcodes. CREATE deploys with a nondeterministic address based on sender and nonce, while CREATE2 allows deterministic addresses using salt.[2] 23. How do you generate random numbers securely on-chain? Avoid block.timestamp or hash; use Chainlink VRF or commit-reveal schemes to prevent miner manipulation.[2] 24. What is a proxy pattern in Solidity? Proxies delegate calls to implementation contracts via DELEGATECALL, enabling upgradable contracts while preserving storage.[2] 25. Explain gas optimization for storage packing. Pack variables into the same 32-byte slot if possible, like uint128 and bool, to reduce storage costs.[2] 26. What is a reentrancy attack and how to prevent it? Reentrancy occurs when external calls allow recursive invocation before state updates; prevent with checks-effects-interactions pattern or reentrancy guards.[6] 27. How many arguments can a Solidity event have? Events can have up to 3 indexed parameters for efficient filtering, with additional non-indexed parameters.[2] 28. Explain delegatecall and its risks. DELEGATECALL executes code in the caller's storage context; risks include storage collisions in proxy patterns.[2] 29. What operations provide partial gas refunds? Deleting mappings/arrays or setting storage to zero refunds gas via SSTORE opcode refunds.[2] 30. In a Salesforce-like SaaS scenario, how would you implement access control for a subscription contract? Use modifiers with role-based access via mappings, ensuring only verified subscribers call premium functions, combined with timestamps for subscription expiry.pragma solidity ^0.8.0;
onlyOwner
uint public balance;
Intermediate Solidity Interview Questions (11-20)
mapping(address => uint) public balances;contract Child is Parent, enabling code reuse and overriding functions.[5]error InsufficientBalance(uint requested, uint available);.[2]receive() external payable for Ether reception.[1]Advanced Solidity Interview Questions (21-30)
