Smart Contracts and dApps Flashcards
7 cards from real Blockchain Technology practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Smart Contracts and dApps flashcards as text
Which vulnerability allowed the 2016 DAO hack, draining ~$60M worth of ETH?
Answer: Reentrancy attack
The DAO hack exploited a reentrancy vulnerability where the attacker's fallback function recursively called withdraw() before the balance was updated.
What does the 'payable' keyword do in a Solidity function?
Answer: Enables the function to receive Ether
The 'payable' modifier allows a Solidity function to receive Ether; without it, any ETH sent to the function will be rejected.
In Ethereum, what is the purpose of the ABI (Application Binary Interface)?
Answer: To define how to encode and decode function calls and data
The ABI defines the encoding scheme for function signatures and parameters, allowing external callers to interact with a deployed smart contract.
Which dApp architecture pattern uses IPFS or Arweave for storing large data off-chain?
Answer: Hybrid storage pattern
The hybrid storage pattern stores large or mutable data on decentralized file systems (IPFS/Arweave) while anchoring only content hashes on-chain.
What is a 'view' function in Solidity?
Answer: A function that reads state but does not modify it
A 'view' function promises not to modify state, so it can be called without a transaction and without spending gas (when called externally).
Which standard defines fungible tokens on Ethereum, used by most DeFi protocols?
Answer: ERC-20
ERC-20 is the standard interface for fungible tokens on Ethereum, defining transfer, approve, and allowance functions used across DeFi.
What problem does the 'checks-effects-interactions' pattern solve in smart contract development?
Answer: Reentrancy vulnerabilities
The checks-effects-interactions pattern prevents reentrancy by updating all state (effects) before calling external contracts (interactions).