Blockchain Developer Certification Practice

What does the unchecked keyword do in Solidity?

1. Prevents arithmetic operations

2. Disables overflow checks within the block

3. Reverts any transaction that overflows

4. Marks variables as safe for arithmetic

The correct answer is: Disables overflow checks within the block

The unchecked keyword in Solidity is used to disable overflow checks for arithmetic operations, which can lead to more efficient execution of code when the developer is certain that an overflow condition cannot occur. By using this keyword, developers relieve the Solidity compiler from performing additional checks for overflow and underflow, thus reducing the overhead that comes with these checks. This is particularly useful in scenarios where performance is critical and the programmer has ensured through code logic that overflow cannot happen, allowing for faster computation while still maintaining safety where necessary. This capability contrasts with the default behavior in Solidity, where arithmetic operations include checks to prevent overflow and underflow, automatically reverting transactions when such conditions occur, which can lead to higher gas costs.