Require, assert, and revert in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the require statement do in a smart contract?

require checks a condition and stops execution if the condition is false. It refunds remaining gas and returns an error message.

intermediate

How is assert different from require?

assert is used to check for conditions that should never be false. If it fails, it consumes all remaining gas and indicates a serious error.

beginner

What happens when revert is called in a smart contract?

revert immediately stops execution, undoes all changes, and refunds remaining gas. It can include a custom error message.

intermediate

When should you use require versus assert?

Use require to check user inputs or external conditions. Use assert to check for internal errors or invariants that should never fail.

advanced

Why is gas refunded when require or revert fails but not when assert fails?

require and revert indicate expected errors and refund gas to save users money. assert signals a critical bug, so it consumes all gas to highlight the problem.

Which statement immediately stops execution and refunds remaining gas if a condition is false?

A continue

B assert

C revert

D require

require stops execution and refunds gas when its condition is false.

Which statement is used to check for conditions that should never happen and consumes all gas if it fails?

A assert

B require

C revert

D throw

assert is for internal errors and consumes all gas on failure.

What does revert do in a smart contract?

A Continues execution ignoring errors

B Stops execution and refunds gas with an optional error message

C Consumes all gas and stops execution

D Logs a warning but continues

revert stops execution, undoes changes, and refunds gas with an error message.

When should you use require in your smart contract?

A To check user inputs and external conditions

B To check internal invariants

C To consume all gas on error

D To log events

require is for validating inputs and external conditions.

Why does assert consume all remaining gas on failure?

A Because it is used for user input validation

B Because it refunds gas to the user

C Because it signals a critical bug that should never happen

D Because it logs an error

assert failures indicate serious bugs, so all gas is consumed to highlight the issue.

Explain the differences between require, assert, and revert in smart contracts.

Think about when each is used and how gas is handled.

When should you use require instead of assert in your code?

Consider the source of the error.