Reading contract state in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'reading contract state' mean in blockchain?

It means checking the current data stored inside a smart contract without changing it. It's like looking at a saved note without erasing or writing anything new.

beginner

Which method is commonly used to read state from a smart contract?

A 'call' method is used to read state. It asks the contract for information without making a transaction or spending gas.

intermediate

Why is reading contract state usually free on blockchains like Ethereum?

Because reading does not change anything on the blockchain, it doesn't require miners to update the chain, so no gas fees are needed.

intermediate

What is the difference between a 'call' and a 'transaction' when interacting with a contract?

'Call' reads data without changing state and costs no gas. 'Transaction' changes state and requires gas fees.

beginner

How can you read a public variable from a smart contract using web3.js?

You use the contract's method for that variable with .call(), like: contract.methods.variableName().call()

What does reading contract state NOT do?

A Retrieve current data from the contract

B Change the data stored in the contract

C Use a call method

D Cost no gas

Reading contract state only retrieves data; it does not change anything.

Which of these is used to read data from a smart contract?

A deploy

B sendTransaction

C mine

D call

The 'call' method reads data without changing the blockchain.

Why does reading contract state usually cost no gas?

A Because it does not change blockchain state

B Because it uses a special token

C Because it is done by miners

D Because it requires a transaction

No gas is needed since reading does not update the blockchain.

In web3.js, how do you read a public variable named 'balance'?

A contract.methods.balance().call()

B contract.methods.balance().send()

C contract.balance()

D contract.call.balance()

The correct syntax uses methods.balance() with .call() to read.

Which statement is true about 'call' and 'transaction'?

A Neither 'call' nor 'transaction' change data

B 'call' changes data; 'transaction' reads data

C 'call' reads data; 'transaction' changes data

D Both 'call' and 'transaction' change data

'call' is for reading; 'transaction' is for writing.

Explain in simple terms how you would read the state of a smart contract without paying gas.

Think about asking a question without changing the answer.

Describe the difference between reading contract state and sending a transaction to a contract.

One is like looking, the other is like writing.