Ethereum Smart Contracts BBLC Practice Questions (Page 7)

Questions 31–35

1. 31application · medium

   A developer is writing a Solidity contract for a token sale. They need to emit a log entry every time a token is purchased, so that off-chain applications can track purchases. Which component should they use?

   • AA state variable that stores the purchase history.
   • BA fallback function that writes to a log file.
   • CA modifier that checks the purchase amount.
   • DAn event that is emitted inside the purchase function.
   Reveal Solution Discussion Select an answer first
2. 32expert · hard

   A smart contract has a state variable that is updated frequently by many users. The team is concerned about the high gas costs of storage writes. Which strategy would most effectively reduce the gas cost per update?

   • AUse a mapping to store the data, and update only the relevant key.
   • BUse a constant variable instead of a state variable.
   • CUse a memory variable to store the data and only write to storage at the end of the transaction.
   • DUse a smaller integer type, such as uint8, to reduce the storage cost.
   Reveal Solution Discussion Select an answer first
4. 33foundation · easy

   In a Solidity smart contract, what is the purpose of a state variable?

   • ATo define the functions that can be called by users.
   • BTo hold temporary data that is cleared after each function call.
   • CTo store data permanently on the blockchain as part of the contract's storage.
   • DTo store the contract's bytecode on the blockchain.
   Reveal Solution Discussion Select an answer first
5. 34application · medium

   A developer is reviewing two smart contract languages for a new project. They need a language that supports complex data structures and is widely supported by tools. They also want to avoid a language that is too restrictive. Which language should they choose?

   • AJavaScript, because it is widely used in web development.
   • BVyper, because it is simpler and more secure.
   • CPython, because it is easy to learn.
   • DSolidity, because it offers rich features and broad tooling support.
   Reveal Solution Discussion Select an answer first
6. 35foundation · easy

   Which of the following is a common security risk in smart contracts where an attacker repeatedly calls a function before the previous call is completed, potentially draining funds?

   • AReentrancy attack
   • BPhishing attack
   • CInteger overflow
   • DDenial of service (DoS)
   Reveal Solution Discussion Select an answer first