Ethereum Smart Contracts BBLC Practice Questions (Page 1)

Questions 1–5

1. 1application · medium

   A user wants to call a function on a smart contract that changes the state of the contract. The user's wallet shows an estimated gas fee. What does this gas fee represent?

   • AThe cost of the computational resources required to execute the function on the Ethereum network.
   • BA deposit that is refunded after the transaction is confirmed.
   • CA fee paid to the contract's owner for using the contract.
   • DA tax imposed by the Ethereum network on all transactions.
   Reveal Solution Discussion Select an answer first
2. 2application · medium

   A user is interacting with a smart contract that has a function which loops over an array of unknown length. The transaction keeps failing with 'out of gas'. What is the most effective way to prevent this issue?

   • ALimit the array length or use a paginated design where the user processes a fixed number of elements per transaction.
   • BRemove the loop and use a recursive function instead.
   • CIncrease the gas limit to the maximum possible value.
   • DUse a storage array instead of a memory array to reduce gas costs.
   Reveal Solution Discussion Select an answer first
4. 3application · medium

   A smart contract has an owner who can change the contract's parameters. The owner's private key is compromised. What is the most effective way to limit the damage?

   • AMake the owner role immutable so that no one can change parameters.
   • BTransfer ownership to a new address immediately after the compromise is detected.
   • CRely on the contract's access control modifier to block the compromised address.
   • DUse a multi-signature wallet for the owner role, so that multiple parties must approve sensitive changes.
   Reveal Solution Discussion Select an answer first
5. 4application · medium

   A developer wrote a Solidity contract for a crowdfunding campaign. The contract has a function that sends Ether to a beneficiary and then updates a 'paid' flag. An auditor warns that the contract is vulnerable to reentrancy. Which change would best mitigate the risk?

   • AMake the function that sends Ether private so only the contract can call it.
   • BUpdate the 'paid' flag before making the external call to the beneficiary.
   • CIncrease the gas limit for the transaction that sends Ether.
   • DUse a low-level call instead of the transfer function to send Ether.
   Reveal Solution Discussion Select an answer first
6. 5foundation · easy

   Which of the following is a typical use case for smart contracts on Ethereum?

   • AProviding a centralized database for a company's internal records.
   • BMining new blocks and validating transactions.
   • CStoring large files like images and videos on the blockchain.
   • DIssuing and managing tokens, such as ERC-20 tokens.
   Reveal Solution Discussion Select an answer first