Checks-Effects-Interactions pattern in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the sender has enough balance before proceeding.

Blockchain / Solidity

require(balances[msg.sender] >= [1], "Insufficient balance");

Drag options to blanks, or click blank then click option'

AtotalSupply

Bmsg.value

Cbalance

Damount

Attempts:

3 left

💡 Hint

Common Mistakes

Using msg.value instead of amount, which is for payable functions.

Using balance or totalSupply which are not the correct variables here.

The require statement checks if the sender's balance is at least the amount they want to send.

2fill in blank

medium

Complete the code to update the sender's balance after the check.

Blockchain / Solidity

balances[msg.sender] [1]= amount;

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A-

B*

C+

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Adding the amount instead of subtracting.

Using multiplication or division operators incorrectly.

We subtract the amount from the sender's balance to reflect the transfer.

3fill in blank

hard

Fix the error in the interaction step to send Ether safely.

Blockchain / Solidity

(bool success, ) = payable(recipient).[1]{value: amount}("");
require(success, "Transfer failed.");

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Asend

Bcall

Ctransfer

Ddelegatecall

Attempts:

3 left

💡 Hint

Common Mistakes

Using transfer which can fail with gas limits.

Using delegatecall which is for different purposes.

Using call is the recommended way to send Ether safely and handle failures.

4fill in blank

hard

Fill both blanks to complete the Checks-Effects-Interactions pattern safely.

Blockchain / Solidity

require(balances[msg.sender] >= [1], "Not enough balance");
balances[msg.sender] [2]= amount;

Drag options to blanks, or click blank then click option'

Aamount

B+

C-

Dmsg.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using msg.value instead of amount in the check.

Adding instead of subtracting the amount.

First, check the sender has enough amount. Then subtract amount from their balance.

5fill in blank

hard

Fill all three blanks to complete the full Checks-Effects-Interactions pattern.

Blockchain / Solidity

require(balances[msg.sender] >= [1], "Insufficient funds");
balances[msg.sender] [2]= [1];
balances[recipient] [3]= [1];

Drag options to blanks, or click blank then click option'

Aamount

B-

C+

Dmsg.value

Attempts:

3 left

💡 Hint

Common Mistakes

Using msg.value instead of amount.

Mixing up addition and subtraction operators.

Check sender has enough amount, subtract it from sender, then add it to recipient.