Solidity Concepts for Contract Development BDC Practice Questions (Page 5)

Questions 21–25

1. 21application · medium

   A supply-chain contract records the transfer of goods between parties. The front-end application needs to display a history of all transfers for a specific product ID. Which approach is most efficient for the front-end to retrieve this data?

   • AStore every transfer in a public array and have the front-end loop through the entire array
   • BUse a state variable to store the latest transfer only
   • CStore transfers in a mapping and have the front-end call a getter for each possible index
   • DEmit an event with the product ID and parties, and have the front-end filter logs by product ID
   Reveal Solution Discussion Select an answer first
2. 22foundation · easy

   Which state mutability modifier indicates that a function does not read or modify the contract's state?

   • Apayable
   • Bconstant
   • Cpure
   • Dview
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4. 23expert · medium

   A developer is auditing a contract that allows users to withdraw their balances. The contract uses a mapping to store balances and a function that sends Ether via call. The developer notices that the balance is updated after the call. What is the most likely vulnerability, and what is the best fix?

   • AReentrancy; update the balance before the call.
   • BPhishing; use a whitelist.
   • CInteger overflow; use SafeMath.
   • DDenial of service; use a pull-payment pattern.
   Reveal Solution Discussion Select an answer first
5. 24foundation · easy

   Which keyword is used to declare an event in Solidity?

   • Aevent
   • Bfunction
   • Cemit
   • Dlog
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6. 25application · medium

   A developer is creating a contract that tracks the status of an order. The status can be Pending, Shipped, Delivered, or Canceled. Which Solidity type should be used to represent the status?

   • AA bool indicating whether the order is active.
   • BA string with the status name.
   • CA uint with constants for each status.
   • DAn enum with the four values.
   Reveal Solution Discussion Select an answer first