Solidity Cheat Sheet 2026

The 30 highest-yield Solidity facts, distilled from real exam questions. Print it, save it as a PDF, or study it here — free, no sign-up.

1. In Solidity 0.8.x, what happens when an arithmetic overflow occurs by default? → The transaction reverts automatically
2. What can the deployer use to run code on the blockchain? → Solidity language
3. What does a Solidity mapping return for a key that has never been set? → The default zero value for the value type
4. What does the reducing length property do? → Delete elements from the array
5. What is the default value of an uninitialized bool state variable in Solidity? → false
6. What is the risk of using `delegatecall` to an untrusted contract? → The callee can overwrite the caller's storage with malicious data
7. What is the purpose of the `receive()` function in Solidity? → It handles plain ETH transfers sent to the contract without calldata
8. Which Solidity type correctly declares a fixed-size byte array of exactly 32 bytes? → bytes32
9. Which attack exploits a contract that calls an external contract before updating its state? → Reentrancy attack
10. What Solidity modifier from OpenZeppelin prevents reentrancy by locking the function? → nonReentrant
11. What vulnerability arises when Solidity arithmetic operations exceed the maximum or minimum value of the data type? → Integer overflow/underflow
12. What are state variables in Solidity stored in? → Slots
13. Who created Ethereum? → Gavin James Wood
14. What happens when `abi.decode` receives data that does not match the specified types? → The transaction reverts with a decoding error
15. What is the name of the property that you can use to delete elements from an array? → Reducing length
16. What do Solidity arrays hold, depending on their size? → Elements
17. What is 'gas griefing' in the context of forwarding gas with `call` in Solidity? → A malicious callee can consume all forwarded gas, causing the caller to run out and revert
18. What happens to variables stored in the memory data location after a Solidity function call ends? → They are erased and the memory is freed
19. What storage slot number is assigned to the first state variable declared in a Solidity contract? → Slot 0
20. What is the purpose of the Proxy Upgrade Pattern (UUPS or Transparent Proxy) in Solidity? → It allows replacing a contract's logic while preserving its storage state and address
21. What data location must be explicitly specified for reference type parameters in Solidity functions? → memory, storage, or calldata
22. What vulnerability is introduced by the `selfdestruct` opcode in Solidity? → It can forcibly send ETH to any contract, breaking balance-based invariants
23. What does Solidity supports? → Reference types and value types
24. What can Solidity contracts use as memory? → Any size
25. Which statement about structs in Solidity is correct? → Structs can contain other structs but not directly recursive self-references
26. What is the key difference between a fixed-size array and a dynamic array in Solidity? → Fixed-size arrays have their length set at compile time while dynamic arrays can grow
27. Which vulnerability allows an attacker to manipulate transaction ordering to their advantage? → Front-running (MEV)
28. What is the byte size of the address type in Solidity? → 20 bytes
29. What does the `safeTransferFrom` function in ERC-721 check that the plain `transferFrom` does not? → Whether the recipient contract implements onERC721Received to confirm it can handle NFTs
30. Which storage location is the cheapest in terms of gas cost in Solidity? → calldata