Flash loans in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start a flash loan using the lending pool.

Blockchain / Solidity

lendingPool.[1](asset, amount, params);

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Awithdraw

Bdeposit

Cborrow

DflashLoan

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'borrow' instead of 'flashLoan' causes the code to fail because 'borrow' is not the flash loan function.

Using 'deposit' or 'withdraw' does not start a flash loan.

The flashLoan function initiates a flash loan in most DeFi lending pools.

2fill in blank

medium

Complete the code to check if the flash loan was repaid within the same transaction.

Blockchain / Solidity

require(amountOwing <= IERC20(asset).balanceOf([1]), "Flash loan not repaid");

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Aaddress(this)

Bbalance

Cmsg.sender

Dtx.origin

Attempts:

3 left

💡 Hint

Common Mistakes

Using msg.sender checks the caller's balance, not the contract's.

Using tx.origin checks the original transaction sender, which is incorrect here.

The contract's token balance is checked using IERC20(asset).balanceOf(address(this)) to ensure repayment.

3fill in blank

hard

Fix the error in the function signature for executing the flash loan logic.

Blockchain / Solidity

function executeOperation(address asset, uint256 amount, uint256 premium, address initiator, bytes calldata [1]) external returns (bool) {

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Aparams

Bdata

Cdetails

Dinfo

Attempts:

3 left

💡 Hint

Common Mistakes

Using other names like 'data' or 'info' causes mismatch with the lending pool interface.

Incorrect parameter names cause compilation errors.

The parameter is conventionally named params to hold extra data passed to the function.

4fill in blank

hard

Fill both blanks to calculate the total amount to repay including the premium.

Blockchain / Solidity

uint256 amountOwing = amount [1] premium [2];

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A+

B-

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' subtracts the premium, which is incorrect.

Using '*' or '/' causes wrong calculations.

The total amount owed is the sum of the borrowed amount and the premium, so both blanks use '+'.

5fill in blank

hard

Fill all three blanks to approve the lending pool to withdraw the owed amount.

Blockchain / Solidity

IERC20(asset).[1](address([2]), [3]);

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Aapprove

BlendingPool

CamountOwing

Dtransfer

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'transfer' instead of 'approve' causes errors.

Approving the wrong address or amount causes the flash loan to fail.

The contract must approve the lending pool to withdraw the owed amount using approve.