ERC-20 implementation in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the ERC-20 standard in blockchain?

ERC-20 is a set of rules that Ethereum tokens follow to work well with wallets and exchanges. It defines how tokens can be transferred and how to keep track of balances.

beginner

Name two required functions in an ERC-20 token contract.

The two required functions are transfer(address to, uint256 amount) to send tokens, and balanceOf(address owner) to check how many tokens an address has.

intermediate

What does the approve function do in ERC-20?

It lets a token owner allow another address to spend tokens on their behalf, up to a set limit.

intermediate

Why is the Transfer event important in ERC-20 tokens?

It helps wallets and apps track token movements by listening to these events, so users see updated balances.

beginner

What is the purpose of the allowance function?

It shows how many tokens an owner allowed a spender to use. This helps control spending limits.

Which function transfers tokens from the caller to another address?

A balanceOf

B approve

C allowance

D transfer

The transfer function sends tokens from the caller to a specified address.

What does the approve function allow?

A Allow another address to spend tokens

B Check token balance

C Transfer tokens directly

D Destroy tokens

approve lets a token owner give permission to another address to spend tokens.

Which event signals that tokens have moved between addresses?

A Approval

B Mint

C Transfer

D Burn

The Transfer event is emitted when tokens move from one address to another.

What does the allowance function return?

A Total token supply

B Tokens approved for spending by a spender

C Balance of an address

D Number of transfers made

allowance shows how many tokens a spender is allowed to use from an owner.

Which of these is NOT part of the ERC-20 standard?

A mint

B balanceOf

C transfer

D approve

mint is not required by ERC-20; it is an optional function for creating new tokens.

Explain the main functions and events that an ERC-20 token contract must have.

Think about how tokens move, how balances are checked, and how spending permissions work.

Describe how the approve and transferFrom functions work together in ERC-20 tokens.

Consider the roles of owner and spender in token transfers.